A method for controlling the stability of arc additive forming droplet transfer of heavy rare earth magnesium alloy

Abstract

This invention discloses a method for controlling the droplet transition stability in arc additive manufacturing of heavy rare earth magnesium alloys, belonging to the field of metal additive manufacturing technology. The method utilizes a Hall current sensor and voltage acquisition module to measure the arc current and voltage waveforms in real time; employs a high-speed camera system to synchronously acquire the entire process of droplet formation, necking, and transition; a controllable heating device is installed below the substrate for constant-temperature preheating to adjust the temperature gradient between the substrate and the droplet; the arc electrical signal and high-speed image signal are input into the human-machine interface software in the industrial control computer, analyzed based on waveform and visual characteristics, and the welding current, wire feed speed, and arc voltage are adjusted in real time to achieve closed-loop control of the droplet transition frequency and morphology. This invention's control method can effectively suppress droplet spatter and short-circuit instability, improve the periodic consistency of droplet transition and interlayer forming quality, and achieve high stability and high precision control in the arc additive manufacturing process of heavy rare earth magnesium alloys.

Description

Technical Field

[0001] This invention relates to the field of metal additive manufacturing technology, specifically to a method for controlling the stability of droplet transition in arc additive forming of heavy rare earth magnesium alloys, which falls under the category of stability control technology in magnesium alloy arc additive manufacturing process. Background Technology

[0002] Magnesium alloys, due to their low density, high specific strength, and excellent damping properties, have broad application prospects in aerospace, defense equipment, and transportation. However, traditional casting or deformation processes often suffer from problems such as microstructure segregation, hot cracking, and low forming accuracy when manufacturing large and complex components, making it difficult to meet the manufacturing requirements of high-performance structural parts.

[0003] Wire Arc Additive Manufacturing (WAAM), a high-efficiency and low-cost metal additive manufacturing technology, enables the rapid prototyping of large metal components. It melts magnesium alloy wire using an electric arc heat source, stacking it layer by layer to form a dense microstructure. However, due to the low melting point, high thermal conductivity, and strong oxidizing activity of magnesium alloys, problems such as unstable droplet transfer, severe spatter, and poor weld fusion are prone to occur during WAAM, seriously affecting the forming quality and microstructure uniformity.

[0004] Especially in the arc additive manufacturing process of heavy rare earth magnesium alloys (such as Mg-Gd-Y series), while the addition of rare earth elements can improve grain refinement and reduce the tendency for hot cracking, it also alters the molten pool viscosity, surface tension gradient, and arc force distribution, leading to a more complex droplet transfer process. The droplet transfer morphology (short-circuit transfer, free transfer, jet transfer, etc.) and its stability directly determine the interlayer forming quality and geometric accuracy. If the droplet transfer is unstable, it will cause problems such as weld fluctuations, uneven forming layers, increased porosity, and spatter.

[0005] Existing technologies mainly rely on empirical control by adjusting parameters such as welding current, arc voltage, and wire feed speed. However, this method is difficult to achieve real-time stable adjustment of the dynamic behavior of molten droplets, and the optimal process window varies greatly under different rare earth contents and the number of forming layers, resulting in insufficient process stability.

[0006] Therefore, there is an urgent need for a control method that can adjust the arc heat input and droplet transition characteristics in real time, so as to stabilize the droplet transition and improve the forming quality during the arc additive forming of heavy rare earth magnesium alloys. Summary of the Invention

[0007] The purpose of this invention is to provide a method for controlling the droplet transition stability in arc additive forming of heavy rare earth magnesium alloys based on Hall sensors, current and voltage signals and high-speed visual feedback. At the same time, by synergistically regulating the arc heat input, dynamic characteristics of the molten pool and wire feeding behavior, the droplet transition is stabilized, spatter and segregation defects are reduced, thereby significantly improving the arc additive forming quality of heavy rare earth magnesium alloys.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A method for controlling the droplet transfer stability in arc additive forming of heavy rare earth magnesium alloys includes the following steps: 1) Establish an arc additive manufacturing system consisting of a pulsed arc power supply, a wire feeding system, a substrate preheating device, a high-speed camera system, a Hall current and voltage detection module, and an industrial control computer; 2) Utilize a high-speed camera system to simultaneously capture the entire process of droplet growth, necking, transition, and splashing; 3) A controllable heating device is installed under the substrate to preheat the substrate at a constant temperature, reduce the temperature gradient between the substrate and the molten droplet, alleviate thermal stress concentration, reduce the tendency of molten droplet rebound and cold cracking, and improve the wetting and stability of the molten droplet. 4) The human-computer interaction software in the industrial control computer is used to comprehensively analyze the characteristic parameters of the electric arc signal and the high-speed camera image data. Based on the waveform characteristics and visual characteristics of the electric arc signal, the real-time determination of the droplet transfer behavior is realized. Then, the welding process parameters of welding current, wire feeding speed and electric arc voltage are adjusted in real time to realize closed-loop control of the droplet transfer cycle and morphology.

[0009] Furthermore, in step 1), the Hall current sensing module in the Hall current and voltage detection module is installed outside the output circuit of the pulse arc power supply and the welding torch power supply cable. The voltage acquisition module in the Hall current and voltage detection module is connected in parallel with the pulse arc power supply for non-contact detection of arc current and voltage waveforms. The output signal is filtered and amplified before being input into the industrial control computer to obtain the characteristic parameters of the arc signal during the droplet growth stage, including current, voltage, fluctuation frequency and short circuit duration. These arc signals reflect the transient state of droplet necking and shedding.

[0010] Furthermore, in step 1), the industrial control computer displays and saves the current and voltage data generated during the arc additive manufacturing process in real time through human-machine interaction software. The human-machine interaction software has data recording and playback functions, which are used to store the waveform, image and temperature data of the arc current and voltage for subsequent analysis and process optimization.

[0011] Furthermore, in step 1), the electric arc additive forming system is also equipped with a gas protection device to form an inert atmosphere in the electric arc zone to prevent the magnesium alloy from oxidizing.

[0012] Furthermore, the gas protection device provides high-purity (≥99.99%) pure argon or an argon-helium mixture (Ar to He volume ratio of 3:1-1:1) as the protective gas. The gas flow rate is typically controlled within the range of 15~25 L / min, and a laminar protective gas curtain is formed through the gas nozzle of the welding torch, effectively covering the molten pool and the heat-affected zone.

[0013] Furthermore, in step 2), the high-speed camera system is set to a frame rate of 2000-4000 frames / second, an exposure time of 1-10 microseconds, and is equipped with an optical filter and a ring laser light source to acquire high-contrast droplet transition images.

[0014] Furthermore, in step 2), the high-speed camera system can use a high-speed camera, which together with an optical filter and a ring laser light source to form a high-speed camera system.

[0015] Furthermore, in step 3), the controllable heating device is a resistance heating plate or an infrared ceramic heating plate, preferably an aluminum-based ceramic heating plate. It is equipped with a thermocouple and a temperature control module to form a controllable heating device. The temperature is fed back to the temperature control module through the thermocouple, and then the temperature control module adjusts the power of the heating plate to achieve closed-loop precise control of the substrate temperature.

[0016] Furthermore, in step 3), the substrate preheating temperature is 100~250℃.

[0017] Furthermore, the determination rule in step 4) is: When the arc voltage fluctuation is detected to exceed ±10%, and high-speed camera image analysis reveals that the molten droplet detaches before it has grown sufficiently, it is determined that the molten droplet transition is too fast. When the arc voltage peak interval is detected to exceed the set threshold of 25-35 ms, and the molten droplet in the high-speed camera image shows an obvious asymmetric hanging shape, it is determined to be a molten droplet transition hysteresis. When the arc voltage fluctuation is controlled within ±8 to 10%, and the droplet necking position is stable, the detachment process is continuous, and there is no obvious splashing in the high-speed camera image, the droplet transition is considered stable.

[0018] Furthermore, the real-time adjustment operation based on the judgment is as follows: When it is determined that the transition is too fast, reduce the wire feeding speed or fine-tune the arc current; When a transition lag is detected, the wire feeding speed is increased or pulse current compensation is applied to adjust the droplet transition frequency.

[0019] Furthermore, in step 4), the welding process parameters include: current 80-200 A, voltage 11-20 V, wire feed speed 6-14 m / min, and welding torch moving speed 6-12 mm / s.

[0020] Furthermore, the control method described above can achieve stable droplet transition and reduce droplet splashing.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The control method of the present invention achieves real-time sensing and adjustment of droplet transition behavior by synchronously acquiring electrical signals from Hall elements and high-speed vision.

[0022] 2. In the control method of the present invention, substrate preheating can effectively reduce the temperature gradient between the substrate and the molten droplet, and avoid molten droplet splashing.

[0023] 3. The droplet transition regularity is enhanced in the control method of the present invention, and the interlayer bonding is more complete.

[0024] 4. The control method of this invention can effectively suppress droplet splashing and short-circuit instability, improve the periodic consistency of droplet transition and the quality of interlayer forming, and achieve high stability and high precision control in the arc additive manufacturing process of heavy rare earth magnesium alloys. Attached Figure Description

[0025] Figure 1 This is a real-life image of the droplet transfer process during the arc additive forming of heavy rare earth magnesium alloy, taken by a high-speed camera system when pulse correction parameter 3 is used in Embodiment 2 of the present invention. Figure 1 (a) shows the rapid growth of the molten droplet during the peak phase of the pulse current; Figure 1 (b) shows the state where the molten droplet continues to grow and hangs down under the influence of gravity; Figure 1 (c) represents the critical state in which the molten droplet and the molten pool are about to come into contact; Figure 1 (d) is the initial state of a controlled short circuit where the molten droplet contacts the molten pool and forms a liquid metal bridge; Figure 1 (e) is the state in which the liquid metal bridge necks and achieves low-kinetic-energy droplet transfer under the action of current reduction and wire retraction. Figure 1 (f) is the state in which the molten droplet has completely transitioned into the molten pool and the end of the welding wire has separated from the molten pool; Figure 1 (g) is the state in which the arc reignites after the short circuit is removed and a new round of droplet formation begins; Figure 1 (h) represents the state where the droplet grows rapidly again after entering the next pulse cycle; Figure 2 This is a waveform diagram of current and voltage collected during the arc additive manufacturing process of heavy rare earth magnesium alloy when pulse correction parameter 3 is used in Embodiment 2 of the present invention. Figure 3 This is a real-life image of the droplet transfer process during the arc additive forming of heavy rare earth magnesium alloy, taken by a high-speed camera system when pulse correction parameter 5 is used in Embodiment 2 of the present invention. Figure 3 (a) shows the rapid growth of the molten droplet during the peak phase of the pulse current; Figure 3 (b) shows the state where the molten droplet continues to grow and hangs down under the influence of gravity; Figure 3 (c) represents the critical state in which the molten droplet and the molten pool are about to come into contact; Figure 3 (d) is the initial state of a controlled short circuit where the molten droplet contacts the molten pool and forms a liquid metal bridge; Figure 3 (e) is the state in which the liquid metal bridge necks and achieves low-kinetic-energy droplet transfer under the action of current reduction and wire retraction. Figure 3 (f) is the state in which the molten droplet has completely transitioned into the molten pool and the end of the welding wire has separated from the molten pool; Figure 3 (g) is the state in which the arc reignites after the short circuit is removed and a new round of droplet formation begins; Figure 3 (h) represents the state where the droplet grows rapidly again after entering the next pulse cycle. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific embodiments. The embodiments of the present invention are merely illustrative examples, and those skilled in the art can make appropriate adjustments to the structure or parameters without departing from the spirit and essence of the present invention, all of which fall within the protection scope of the present invention. Example 1

[0027] This embodiment provides a method for controlling the droplet transfer stability in arc additive forming of heavy rare earth magnesium alloys, including the following steps: 1) Establish an arc additive manufacturing system consisting of a pulsed arc power supply, a wire feeding system, a substrate preheating device, a high-speed camera system, a Hall current and voltage detection module, and an industrial control computer; 2) Utilize a high-speed camera system to simultaneously capture the entire process of droplet growth, necking, transition, and splashing; 3) A controllable heating device is installed under the substrate to preheat the substrate at a constant temperature, reduce the temperature gradient between the substrate and the molten droplet, alleviate thermal stress concentration, reduce the tendency of molten droplet rebound and cold cracking, and improve the wetting and stability of the molten droplet. 4) The human-computer interaction software in the industrial control computer is used to comprehensively analyze the characteristic parameters of the electric arc signal and the high-speed camera image data. Based on the waveform characteristics and visual characteristics of the electric arc signal, the real-time determination of the droplet transfer behavior is realized. Then, the welding process parameters of welding current, wire feeding speed and electric arc voltage are adjusted in real time to realize closed-loop control of the droplet transfer cycle and morphology.

[0028] In this embodiment, the arc additive manufacturing system includes a FANUC CMT Advanced 4000R welding machine, a FANUC M-20Id / 25 six-axis robot, a welding torch, a dual-axis 500kg servo positioner, a VR 4000Case / D300 / 4R / G / W / F++ wire feeder, an RCU5000i control panel, and an industrial computer. A Hall effect current sensor module is installed outside the welding torch's power cable to detect the arc current signal in real time. A voltage acquisition module is connected in parallel with the welding power supply via a voltage divider circuit to synchronously acquire the arc voltage waveform signal. The current and voltage signals are input to the industrial computer via an analog-to-digital converter for real-time waveform characteristic analysis.

[0029] In this embodiment, a high-speed camera system is positioned in front of the welding torch. The system combines a high-speed camera (such as a high-speed camera from a certain brand) with an optical filter and a laser ring light source to record the entire process of droplet generation, necking, separation, and flight at a frame rate of 2000-4000 frames per second and an exposure time of 1-10 microseconds. Specifically: the high-speed camera is fixed to the side and front of the welding torch's trajectory, with its lens facing the droplet transition area; the laser ring light source is coaxially mounted at the front of the camera lens, and its ring beam can uniformly illuminate the droplet and arc area around the camera's field of view; the optical filter is mounted in front of the camera lens, typically a narrow-band filter (such as a center wavelength of 808 nm or 532 nm) or a neutral density (ND) filter, used to significantly filter out the intense visible light (especially ultraviolet and infrared interference light) generated by the arc itself, while allowing specific wavelengths of the laser light source to pass through. The laser ring light source emits high-intensity, highly coherent monochromatic light (such as 808 nm infrared laser or 532 nm green laser), which illuminates the surface of the molten droplet and produces diffuse reflection. The optical filter only allows light near the laser wavelength to enter the camera, thereby almost completely shielding the arc light, making the molten droplet outline appear as a high-contrast bright area in the image, while the background is a dark field. This combination of "laser backlight / side lighting + narrowband filter" can clearly capture the outline, necking, detachment moment and splash trajectory of the molten droplet, and obtain stable images even under strong arc interference.

[0030] The laser source and camera exposure signal can be synchronized via an external trigger or industrial computer to ensure that the laser pulse illuminates within a very short time (1-10 microseconds) of camera exposure, further suppressing ambient light interference. The acquired image sequence is transmitted to the industrial computer in real time for subsequent droplet morphology analysis and transition frequency calculation.

[0031] In this embodiment, the substrate preheating device is placed below the substrate, employing a resistance heating plate or a ceramic infrared heater (such as an aluminum-based ceramic heating plate), and equipped with thermocouples to form a closed-loop temperature control system. Specifically, the thermocouples are attached to or embedded in the lower surface of the substrate (or the surface of the heating plate) to measure the actual temperature of the substrate in real time and transmit the temperature signal to the temperature control module. The temperature control module (such as a PID temperature controller) receives the feedback signal from the thermocouples and compares it with a preset target temperature value. Based on the comparison result, the temperature control module dynamically controls the current (or duty cycle) supplied to the heating plate through power adjustment elements such as solid-state relays (SSRs) or silicon controlled rectifiers, thereby precisely adjusting the heating power of the heating plate. Through this closed-loop feedback, the system can stabilize the substrate temperature within a preset range, achieving constant-temperature preheating and effectively reducing the temperature gradient between the substrate and the molten droplets. Simultaneously, insulation cotton or ceramic insulation material is used to cover the perimeter of the substrate to maintain a stable thermal field. The preheating temperature range is 100–250°C, with a temperature control accuracy of ±2°C. Preheating the substrate can reduce the temperature gradient between the substrate and the molten droplet, improve the wettability and spreadability of the molten droplet, and reduce thermal stress concentration.

[0032] In this embodiment, the arc additive manufacturing system also includes a gas protection device, which uses high-purity argon gas (purity ≥99.99%) and sets the gas flow rate to 25 L / min to form a uniform protective gas curtain through the welding torch nozzle.

[0033] During operation, the Hall current sensor and voltage acquisition module transmit current and voltage signals to the data acquisition card, which then transmits the digital signals to the industrial control computer. The industrial control computer displays and saves this data in real time through human-machine interface software. The high-speed camera system synchronously records the transition image sequence of the molten droplet and sends it to the industrial control computer for analysis of droplet morphology changes and transition frequency.

[0034] Based on the analysis results of electrical and image signals, the droplet transition state is determined: When the arc voltage fluctuation is detected to exceed ±10%, and high-speed camera image analysis reveals that the molten droplet detaches before it has grown sufficiently, it is determined that the molten droplet transition is too fast. When it is determined that the transition is too fast, the wire feed speed is reduced or the arc current is finely adjusted. When the arc voltage peak interval is detected to exceed the set threshold of 25-35 ms, and the droplet in the high-speed camera image shows an obvious asymmetrical hanging shape, it is determined that the droplet transition hysteresis is present. When it is determined to be transition hysteresis, the wire feed speed is increased or pulse current compensation is applied to adjust the droplet transition frequency. When the arc voltage fluctuation is controlled within ±8 to 10%, and the droplet necking position is stable, the detachment process is continuous, and there is no obvious splashing in the high-speed camera image, the droplet transition is considered stable.

[0035] Among them, the image processing algorithm can use background subtraction and edge detection algorithms to extract the droplet contour and calculate its centroid position, necking width, overhang asymmetry and other features; after low-pass filtering (cutoff frequency 1kHz) of the current and voltage signals, features such as short-time root mean square value, fluctuation standard deviation and short-circuit event count are extracted; the image features and electrical signal features are input into a rule-based state machine to realize real-time classification of the droplet transition state (stable / too fast / lagging).

[0036] In this embodiment of the invention, the welding process parameters are set as follows: current 80–200 A, voltage 11–20 V, wire feed speed 6–14 m / min, and welding torch moving speed 6–12 mm / s. Within this parameter range, a relatively stable droplet transfer behavior can be obtained through the synergistic effect of substrate preheating and real-time control.

[0037] Experimental results show that when the substrate temperature is controlled within the range of 150 to 250°C, the droplet morphology is relatively stable and the arc voltage waveform has good periodicity.

[0038] The control method of this invention achieves real-time sensing and adjustment of droplet transition behavior through synchronous acquisition of Hall element electrical signals and high-speed vision. The specific workflow is as follows: The arc current and voltage signals are acquired in real time using a Hall sensor, and the sequence of molten droplet images is acquired synchronously using a high-speed camera system. The image processing module in the industrial control computer performs real-time segmentation and feature extraction on the molten droplet image (including droplet growth, necking, transition, and splash trajectory, etc.); the signal processing module performs filtering, peak detection, and short-time Fourier analysis on the current and voltage waveforms to extract features such as fluctuation amplitude, frequency, and short-circuit duration. Based on preset judgment rules (such as voltage fluctuation amplitude, peak interval, image symmetry, etc.), combined with historical data and real-time characteristics, the droplet transition state (too fast, lag, stable) is judged. Based on the judgment results, parameters such as wire feeding speed, pulse current frequency, and substrate heating power are adjusted in real time through PID control algorithm to achieve dynamic and stable control of droplet transition.

[0039] This invention achieves dynamic control of droplet transfer during arc additive manufacturing by real-time monitoring of Hall current and voltage signals, high-speed visual image analysis, and substrate thermal field modulation. This method effectively suppresses droplet instability and spatter, improving the interlayer bonding quality and forming consistency of heavy rare-earth magnesium alloy arc additive manufacturing. Example 2

[0040] The control process for droplet transfer stability in arc additive forming of Mg-9Gd-3Y-1Zn-0.6Zr heavy rare earth magnesium alloy, based on the control method in Example 1, is as follows: (1) Based on the electric arc additive forming system of Example 1, electric arc additive forming was carried out using Mg-9Gd-3Y-1Zn-0.6Zr heavy rare earth magnesium alloy wire with a diameter of 1.2 mm; (2) Adjust the substrate preheating temperature to 200±2℃; (3) In the process of arc additive manufacturing, the welding process parameters used are: wire feed speed 12 m / min, welding torch moving speed 10 mm / s, and the pulse correction parameters are set to 3 and 5 respectively for comparative tests.

[0041] The "pulse correction parameter" referred to in this invention is a waveform modulation parameter built into the pulsed arc power supply, used to adjust the peak value, base time ratio, and rise / fall slope of the pulse current. Its value range is typically 1 to 10. A larger value results in more concentrated pulse energy and stronger arc force, suitable for thick plates or high-viscosity molten pools; a smaller value results in a smoother pulse energy distribution, suitable for thin plates or low-viscosity molten pools. In this invention, by adjusting the pulse correction parameter in real time, the droplet stress state and transition frequency can be synergistically controlled, especially under the conditions of high-viscosity molten pools of heavy rare earth magnesium alloys, achieving a smooth droplet transition.

[0042] In the process of arc additive manufacturing, if there are large arc fluctuations or uneven droplet transitions, the arc can be stabilized and the droplet transition can be smoothly controlled by appropriately adjusting the welding current, voltage, or pulse correction parameters.

[0043] Based on the above control process, a high-speed camera was used to capture images of the droplet transfer behavior during the arc additive manufacturing process of heavy rare earth magnesium alloys. The resulting images of the droplet transfer are shown below. Figure 1 and Figure 3 As shown; simultaneously, the welding current and voltage signals when the pulse correction parameter is 3 are synchronously acquired, and their waveforms are shown in the figure. Figure 2 As shown.

[0044] like Figure 1 As shown, when the pulse correction parameter is 3, the high-speed imaging results can clearly capture the continuous and stable droplet transition process (corresponding to...). Figure 1 (ah), the droplet transition frequency distribution is uniform. (Combined) Figure 2 As shown in the electrical signal waveforms, the current and voltage waveforms have good periodicity and uniform peak spacing. The short-circuit stage is characterized by a sudden drop in voltage and a sudden rise in current, indicating that the droplet transfer process is stable and there is less spatter at this time, resulting in high quality of arc additive manufacturing.

[0045] As a comparative example, when the pulse correction parameter is increased to 5, the high-speed imaging results show that the surface fluctuation of the molten pool is significantly enhanced after the droplet enters the molten pool, and the generation of fine spatter particles can be observed, indicating that an excessively large pulse correction parameter is not conducive to the control of droplet transition stability.

[0046] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for controlling the droplet transfer stability in arc additive manufacturing of heavy rare earth magnesium alloys, characterized in that, The control method includes the following steps: 1) Establish an arc additive manufacturing system consisting of a pulsed arc power supply, a wire feeding system, a substrate preheating device, a high-speed camera system, a Hall current and voltage detection module, and an industrial control computer; 2) Utilize a high-speed camera system to simultaneously capture the entire process of droplet growth, necking, transition, and splashing; 3) A controllable heating device is installed under the substrate to preheat the substrate at a constant temperature, reduce the temperature gradient between the substrate and the molten droplet, alleviate thermal stress concentration, reduce the tendency of molten droplet rebound and cold cracking, and improve the wetting and stability of the molten droplet. 4) The human-computer interaction software in the industrial control computer is used to comprehensively analyze the characteristic parameters of the electric arc signal and the high-speed camera image data. Based on the waveform characteristics and visual characteristics of the electric arc signal, the real-time determination of the droplet transfer behavior is realized. Then, the welding process parameters of welding current, wire feeding speed and electric arc voltage are adjusted in real time to realize closed-loop control of the droplet transfer cycle and morphology.

2. The control method according to claim 1, characterized in that, In step 1), the Hall current sensing module in the Hall current and voltage detection module is installed outside the output circuit of the pulse arc power supply and the welding torch power supply cable. The voltage acquisition module in the Hall current and voltage detection module is connected in parallel with the pulse arc power supply for non-contact detection of arc current and voltage waveforms. The output signal is filtered and amplified before being input into the industrial control computer to obtain the characteristic parameters of the arc signal during the droplet growth stage, including current, voltage, fluctuation frequency and short circuit duration. These arc signals reflect the transient state of droplet necking and shedding.

3. The control method according to claim 1, characterized in that, In step 1), the electric arc additive forming system is also equipped with a gas protection device to form an inert atmosphere in the electric arc zone to prevent the magnesium alloy from oxidizing.

4. The control method according to claim 1, characterized in that, In step 2), the high-speed camera system is set to a frame rate of 2000-4000 frames / second, an exposure time of 1-10 microseconds, and is equipped with an optical filter and a ring laser light source to acquire high-contrast images of molten droplet transition.

5. The control method according to claim 1, characterized in that, In step 3), the controllable heating device is a resistance heating plate or an infrared ceramic heating plate. It is equipped with a thermocouple and a temperature control module to form a controllable heating device. The temperature is fed back to the temperature control module through the thermocouple, and then the temperature control module adjusts the power of the heating plate to achieve closed-loop precise control of the substrate temperature.

6. The control method according to claim 1 or 5, characterized in that, In step 3), the substrate preheating temperature is 100~250℃.

7. The control method according to claim 1, characterized in that, The determination rule in step 4) is as follows: When the arc voltage fluctuation is detected to exceed ±10%, and high-speed camera image analysis reveals that the molten droplet detaches before it has grown sufficiently, it is determined that the molten droplet transition is too fast. When the arc voltage peak interval is detected to exceed the set threshold of 25-35 ms, and the molten droplet in the high-speed camera image shows an obvious asymmetric hanging shape, it is determined to be a molten droplet transition hysteresis. When the arc voltage fluctuation is controlled within ±8 to 10%, and the droplet necking position is stable, the detachment process is continuous, and there is no obvious splashing in the high-speed camera image, the droplet transition is considered stable.

8. The control method according to claim 7, characterized in that, Based on the assessment, the real-time adjustment operation is as follows: When it is determined that the transition is too fast, reduce the wire feeding speed or fine-tune the arc current; When a transition lag is detected, the wire feeding speed is increased or pulse current compensation is applied to adjust the droplet transition frequency.

9. The control method according to claim 1, characterized in that, In step 4), the welding process parameters include: current 80-200 A, voltage 11-20 V, wire feed speed 6-14 m / min, and welding torch moving speed 6-12 mm / s.

Images