An electric arc wire feed additive manufacturing compensation device and method based on wire end monitoring

Abstract

A method and apparatus for compensation in arc-melted wire additive manufacturing based on wire end monitoring belongs to the field of additive manufacturing. The method involves pre-setting a wire end movement constraint boundary within the arc thermal field, adjusting the camera's field of view to ensure the wire end is within the camera's view, and then monitoring the position of the wire end using the camera. Based on the camera's monitoring, a control system is established. The control system's function is to constrain the movement of the wire end during the arc-melted wire manufacturing process by fine-tuning the wire feeding speed, thereby making the arc-melted wire forming more stable. This method, by setting a wire end movement constraint boundary and utilizing camera monitoring and feedback control to constrain the wire end, achieves monitoring and compensation of the arc-melted wire process, ensuring the stability of the forming quality, and has the advantages of strong universality and high control precision.

Description

Technical Field

[0001] This invention relates to a compensation device and method for arc-fuse additive manufacturing based on wire end monitoring, belonging to the fields of system control technology and arc-fuse additive manufacturing technology. Background Technology

[0002] Wax-wire additive manufacturing (WAAM) is a key technology for achieving intelligent manufacturing. Compared with other additive technologies, WAAM has advantages such as rapid prototyping, high efficiency, and low cost, and has wide applications in aerospace, automotive, and energy industries. However, WAAM is highly sensitive to disturbances during the additive manufacturing process, which can lead to significant deficiencies in material forming accuracy and stability, such as porosity, excessively large molten pool, and workpiece deformation due to excessive heat input. These deficiencies severely restrict the development of WAAM technology. Therefore, researching methods to improve the forming stability and disturbance resistance of WAAM technology, and achieving precise forming under complex conditions, is crucial for the mature application of WAAM technology. In recent years, scholars at home and abroad have conducted many studies on the forming control of WAAM technology. Taking the electric arc heat source as an example, some scholars have proposed an alternating electric arc heat source based on pulsed current to control heat input, achieve heat-mass decoupling, and suppress the influence of disturbances on forming, which is of great significance for realizing the forming control of WAAM technology. Taking wire feeding speed as an example, some scholars have proposed a pulsed wire feeding speed control method. This method uses a special wire feeding mechanism to make the wire feeding speed change sinusoidally and periodically to control the droplet transfer. This method can promote the initiative of droplet transfer to a certain extent, but there is no specific reference standard for droplet transfer under different types of arc environments.

[0003] In the WAAM additive manufacturing process, the wire feed speed often has a profound impact on the additive manufacturing quality. During this process, problems may occur such as the wire feed speed being too fast and penetrating the arc, or the wire feed speed being too slow and unable to keep up with the welding gun speed. The position of the wire end determines the transition position of the molten droplet to the molten pool, which is crucial for additive manufacturing. The position of the wire end often needs to be controlled by adjusting the wire feed speed.

[0004] Based on a review of domestic and international research, this invention patent proposes a compensation method and device for arc-fused wire additive manufacturing based on wire end monitoring. With the assistance of a professional camera for monitoring, a feedback control system is established. This system uses an image acquisition device to collect wire end position information to control the wire feeding speed, thereby ensuring that the wire end remains stably within the moving constraint boundary, achieving the goal of controlling the wire end position. Summary of the Invention

[0005] This invention addresses the problem of uncertainty in the position of the wire end caused by the wire feeding speed by setting a moving constraint boundary for the wire end. By controlling the wire feeding speed, it ensures that the wire end always moves within the moving constraint boundary, thereby achieving a more stable arc-fused wire additive manufacturing process.

[0006] The purpose of this invention is to compensate for the instability in additive manufacturing caused by the uncertainty of the filament end position, based on monitoring by a professional camera. Unlike traditional arc-wire additive manufacturing, this method significantly improves the stability and efficiency of the arc-wire additive manufacturing process. The designed control system is a feedback control system that eliminates disturbances by adjusting the wire feed speed. Overall, this control system achieves precise compensation for the filament end movement constraints through adaptive adjustment of the wire feed speed.

[0007] The system device of the present invention: a camera (9) is located next to the end of the wire at the welding torch arc and is used to collect image information of the end position of the wire; the wire is fed by a wire feeding system (2), which includes a wire feeding motor (4) and a digital potentiometer (5), and the wire feeding motor (4) and the digital potentiometer (5) are electrically connected (the wire feeding motor and the digital potentiometer are connected in series in the wire feeding system circuit); the camera (9) is electrically or signal connected to the image acquisition device (10), the image acquisition device (10) is electrically or signal connected to the image processing device (11), the image processing device (11) is electrically or signal connected to the controller (12), and the controller (12) is electrically or signal connected to the digital potentiometer (5);

[0008] The image acquisition device is used to acquire image information of the end of the wire; the image processing device is used to analyze the image information and transmit signals to the controller; the controller performs logical operations on the input signals and outputs signals to control the actuators; the digital potentiometer is used to change the resistance value of the wire feeding system circuit, thereby controlling the wire feeding speed.

[0009] The image acquisition device (10) transmits the image information of the end position of the wire monitored by the camera (9) to the image processing device (11). The image processing device (11) processes and converts the image signal and transmits it to the PLC controller (12). The PLC controller (12) performs logical operation processing on the input signal received and outputs high and low level signals to control the digital potentiometer (5) to change the resistance value of the wire feeding system. By controlling the speed of the wire feeding motor, the purpose of controlling the wire feeding speed is finally achieved.

[0010] The image signal monitored by the camera (9) is transmitted to the image acquisition device (10) through the signal transmission line. The image acquisition device (10) performs microprocessing on the collected image (high-speed acquisition and storage, and image compression) and outputs a signal to the image processing device (11). The image processing device (11) converts the collected image information through the internal integrated circuit and outputs a recognizable signal to the PLC controller (12). The PLC controller (12) performs logical operation on this signal and outputs high and low level signals to the digital control potentiometer (5). The digital control potentiometer (5) realizes the adjustment function of the internal variable resistor by receiving the regular high and low levels output by the PLC.

[0011] When establishing the system device (or establishing the device model), the following is defined:

[0012] (1) The wire is a cylinder with a circular cross-section;

[0013] (2) The end of the wire melts into a sphere under the action of an electric arc;

[0014] (3) Define the arc boundary of the welding torch as the region enclosed by the isotherms corresponding to 95% energy distribution of the arc heat source, and the arc heat source conforms to the Gaussian distribution.

[0015] (4) The wire within the boundary of the electric arc heat source can be completely melted;

[0016] (5) Set the movement constraint boundary of the wire end to be a rectangle or a circle, requiring the wire end to move only within the boundary range;

[0017] (6) The influence of external factors on the electric arc and wire is not considered;

[0018] (7) Ignore the effects of stress-induced precipitation, flow characteristics and phase change thermal properties of the filament;

[0019] (8) The motion of the wire end conforms to rigid body kinematics.

[0020] The method for compensation using the above-mentioned arc-fuse additive manufacturing compensation device based on wire end monitoring is characterized by comprising the following steps:

[0021] (1) Set the boundary of the wire end movement constraint (draw it in the form of lines), adjust the camera focal length so that the camera field of view coincides with the boundary of movement constraint, and ensure that the wire end can be monitored within the camera field of view.

[0022] (2) The camera monitors the position of the filament end. During this process, it is observed whether the filament end is within the camera's field of view. At this time, three situations may occur:

[0023] ① The end point of the wire is within the camera's field of view, meaning the end of the wire is currently inside the movement constraint boundary; therefore, there is no need to change the wire feed speed. (See also...) Figure 2 (a)

[0024] ② The end point of the filament is outside the camera's field of view, but the filament is not within the camera's field of view (i.e., there is no filament within the camera's field of view). This means the end of the filament has not entered the moving constraint boundary. This is due to the filament feeding speed being too slow. It is necessary to reduce the loop resistance to increase the speed of the filament feeding motor, thereby increasing the filament feeding speed. (See also: [link to relevant documentation]) Figure 2 In case (c), the corresponding filament extends beyond the movement constraint boundary and there is no filament within the camera's field of view;

[0025] ③ The end of the filament is outside the camera's field of view; the filament has passed through the entire camera's field of view, meaning the end of the filament exceeds the movement constraint boundary. This is caused by excessive filament feeding speed, requiring an increase in the loop resistance to slow down the filament feeding motor and thus reduce the feeding speed. (See also...) Figure 2 In (b), there is no end of the filament within the camera's field of view, and the rest of the filament passes through the camera's field of view.

[0026] Step (2) is performed in real time during the welding process.

[0027] In the compensation method, the controlled variable is the actual position of the wire end within the movement constraint range, the manipulated variable is the system wire feeding speed, and the input is the signal of the wire end within the movement constraint range.

[0028] The designed system is a feedback system that uses feedback adjustment to constrain the movement of the filament end. This feedback system achieves precise compensation for the movement constraint of the filament end by adaptively adjusting the filament feed speed.

[0029] In this system, the image acquisition device collects and transmits image information monitored by the camera in real time to the image processing device. The image processing device processes the transmitted image information, generating three different identifiable signals from its internal circuitry after processing images of camera monitoring conditions ①, ②, or ③. The image processing device then transmits these signals to the PLC controller for logical operations. After processing the input signals, the PLC controller outputs high and low level signals according to its internal instructions, thereby controlling the resistance value of the digital potentiometer. Changes in the internal resistance value of the wire feeding system alter the speed of the wire feeding motor, thus regulating the wire feeding speed. This feedback process is repeated cyclically to achieve the goal of controlling the wire end point within the moving constraint boundary.

[0030] The present invention can achieve the following beneficial effects:

[0031] This invention relates to a compensation method and apparatus for arc-fed additive manufacturing based on wire end monitoring. A wire end movement constraint compensation device is designed to achieve precise compensation for wire end movement constraints by adaptively adjusting the wire feeding speed. This system comprises a camera, an image acquisition device, an image processing device, a PLC controller, and a digitally controlled potentiometer. The image acquisition device and image processing device control the monitoring and feeding instruments in the control system, the PLC controller acts as the controller in the control system, and the digitally controlled potentiometer acts as the actuator. This feedback system controls the current in the wire feeding system through these devices to adjust the wire feeding speed for acceleration and deceleration. Through repeated feedback adjustment, the system eliminates the influence of system disturbances on wire end movement. Using this compensation method, the wire feeding speed achieves adaptive adjustment, and simultaneously, during arc-fed additive manufacturing, the movement of the wire end is constrained, resulting in more stable arc-fed additive manufacturing. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the arc-fused wire additive manufacturing compensation method and device based on wire end monitoring according to an embodiment of the present invention.

[0033] Figure 2 This is a schematic diagram showing three possible scenarios for the end position of the filament in an embodiment of the present invention.

[0034] Figure 3 This is a control block diagram of the arc-fused wire additive manufacturing compensation method based on wire end monitoring according to the present invention.

[0035] Figure 4 This is a flowchart of the control logic for the arc-fused wire additive manufacturing compensation method based on wire end monitoring, as described in this invention.

[0036] Figure 1 The components are: 1. Welding torch; 2. Wire feeding system; 3. Wire feeding system power supply; 4. Wire feeding motor; 5. Digital potentiometer; 6. Welding power supply; 7. Shielding gas; 8. Shielding gas gauge; 9. Camera; 10. Image acquisition device; 11. Image processing device; 12. PLC controller. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the embodiments. These embodiments are merely preferred implementations of the present invention and are not intended to limit the present invention.

[0038] Step 1: Before welding or additive manufacturing, perform surface treatment on the workpieces to be welded. Use sandpaper to polish each workpiece to remove the oxide film on the surface, then clean with acetone, dry and fix it on the welding fixture.

[0039] Step 2: When using the welding additive platform, connect the gas circuit of the welding system, open the protective gas valve, and turn on all the switches of the welding system as required. Adjust the position of the welding nozzle to the position where welding work will be carried out.

[0040] Step 3: Determine the moving constraint boundary of the filament end. Draw a bounding box with the same size as the moving constraint boundary on the cardboard. Move the cardboard so that the actual moving constraint boundary coincides with the bounding box on the cardboard. Adjust the camera focal length so that the camera's field of view coincides with the bounding box on the cardboard. Adjust the position of the filament end so that it is located in the center of the camera's field of view.

[0041] Step 4: Connect the camera's image output port to the image acquisition device using a signal cable. The image acquisition system will transmit the processed image information from the output port to the input port of the image processing device via the signal cable.

[0042] Step 5: After the image processing device converts the image information into a signal, it connects the output port to the input port of the PLC controller I, and the output port of the PLC controller O is connected to the CS pin of the CNC potentiometer.

[0043] Step Six: After the control components are connected, turn on the wire feeding system switch to begin the arc initiation operation. Observe the position of the wire end using a camera. During the control process, the system control may experience delays, making it impossible to adjust the wire feeding speed in a timely manner. In this case, it is necessary to adjust the control component parameters promptly.

[0044] The above description, in conjunction with specific embodiments, provides a further detailed explanation of the present invention and should not be construed as limiting the specific implementation of the invention to these descriptions. For those skilled in the art, the architectural form of this invention can be flexibly varied without departing from its conceptual framework, leading to the derivation of a series of products. Any simple deductions or substitutions should be considered as falling within the patent protection scope defined by the submitted claims.

Claims

1. A method for compensation using an arc-fused wire additive manufacturing compensation device based on wire end monitoring, characterized in that, The arc welding wire additive manufacturing compensation device includes: a camera (9), which is located next to the end of the wire at the arc of the welding torch, for acquiring image information of the end position of the wire; a wire feeding system (2), which includes a wire feeding motor (4) and a digital potentiometer (5), the wire feeding motor (4) and the digital potentiometer (5) being electrically connected, and the wire being fed by the wire feeding system (2); an image acquisition device (10), for acquiring image information of the end of the wire; an image processing device (11), for analyzing the image information and transmitting signals to the PLC controller; a PLC controller (12), for performing logical operations on the input signals and outputting signals to control the actuators; and a digital potentiometer (5), for changing the resistance value of the wire feeding system circuit, thereby controlling the wire feeding speed. The camera (9) is electrically or signal-connected to the image acquisition device (10), the image acquisition device (10) is electrically or signal-connected to the image processing device (11), the image processing device (11) is electrically or signal-connected to the PLC controller (12), and the PLC controller (12) is electrically or signal-connected to the digital potentiometer (5). The image acquisition device (10) transmits the image information of the end position of the wire monitored by the camera (9) to the image processing device (11). The image processing device (11) processes and converts the image signal and transmits it to the PLC controller (12). The PLC controller (12) receives the input signal, performs logical operation processing, and outputs high and low level signals to control the digital potentiometer (5) to change the resistance value of the wire feeding system. By controlling the speed of the wire feeding motor, the purpose of controlling the wire feeding speed is finally achieved. The method includes the following steps: (1) Set the moving constraint boundary of the wire end, adjust the camera focal length so that the camera field of view coincides with the moving constraint boundary, and ensure that the situation of the wire end can be monitored within the camera field of view; (2) The camera monitors the position of the end of the filament. During this process, it observes whether the end of the filament is within the camera's field of view. At this time, three situations may occur: ① The end point of the wire is within the camera's field of view, that is, the end of the wire is inside the movement constraint boundary at this time, so there is no need to change the wire feeding speed; ② The end point of the filament is outside the camera's field of view, but the filament is not within the camera's field of view, meaning there is no filament within the camera's field of view. This is because the filament end has not entered the moving constraint boundary. This is caused by the filament feeding speed being too slow. It is necessary to reduce the loop resistance to increase the speed of the filament feeding motor and thus increase the filament feeding speed. In other words, the corresponding filament exceeds the moving constraint boundary and there is no filament within the camera's field of view. ③ The end of the wire is outside the camera's field of view, and the wire passes through the entire camera's field of view. That is, the end of the wire exceeds the movement constraint boundary at this time. This is caused by the wire feeding speed being too fast. It is necessary to increase the circuit resistance to slow down the wire feeding motor and thus reduce the wire feeding speed. That is, there is no end of the wire in the corresponding camera's field of view, and the other part of the wire passes through the camera's field of view. Step (2) is performed in real time during the welding process.

2. The method of claim 1, wherein the method is compensated by using an electric arc wire additive manufacturing compensation device based on a wire end monitoring, wherein The image signal monitored by the camera (9) is transmitted to the image acquisition device (10) through the signal transmission line. The image acquisition device (10) performs microprocessing on the collected image and outputs a signal to the image processing device (11). The image processing device (11) converts the collected image information through the internal integrated circuit and outputs a recognizable signal to the PLC controller (12). The PLC controller (12) performs logical operations on this signal and outputs high and low level signals to the digital potentiometer (5). The digital potentiometer (5) realizes the adjustment function of the internal variable resistor by receiving the regular high and low level signals output by the PLC controller (12).

3. The method of claim 2, wherein the method is compensated by using an electric arc wire feedstock end monitoring based electric arc wire additive manufacturing compensation device, characterized in that, In the method, the controlled variable is the actual position of the filament end within the movement constraint range, the manipulated variable is the system filament feeding speed, and the input is the signal of the filament end within the movement constraint range.

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