Method and device for predicting the state of a molten pool during continuous variable positioning of a variable polarity plasma arc welding

Abstract

The application discloses a method and device for predicting and controlling the state of a molten pool during continuous variable-position welding of a variable-polarity plasma arc, and a model of a convolutional neural network + long short-term memory neural network (CNN + LSTM) is used to predict the included angle of the rear wall of a small-hole molten pool. When the predicted included angle of the rear wall of the small-hole molten pool exceeds the threshold range of the included angle of the rear wall of the small-hole molten pool, the rear wall point is quickly fed with a wire, so that the included angle of the rear wall of the small-hole molten pool is within the corresponding threshold range, and the instability of the small-hole molten pool is prevented in advance and good weld forming quality is ensured.

Description

Technical Field

[0001] This invention relates to the field of welding quality control methods, and in particular to a method for predicting and controlling the state of the molten pool during continuous position changes in variable polarity plasma arc welding. Background Technology

[0002] Variable polarity plasma arc welding is a fusion welding method that uses a high-energy-density plasma arc beam as the welding heat source. It features concentrated energy, high productivity, fast welding speed, low stress deformation, and stable arc. Variable polarity through-hole plasma arc welding is a new, highly efficient, zero-defect welding method developed for aluminum alloys. Due to the presence of a keyhole weld pool, its optimal welding position is vertical. However, for large aluminum alloy structural parts, the workpiece is difficult to move and rotate, requiring changes in the welding torch position to achieve all-position welding. In non-vertical welding positions, variable polarity plasma arc welding is prone to keyhole instability, leading to defects such as cutting. Summary of the Invention

[0003] This invention provides a method for predicting and controlling the state of the molten pool during continuous position changes in variable polarity plasma arc welding, in order to improve welding quality.

[0004] This invention provides a method for predicting and controlling the state of the molten pool during continuous position change in variable polarity plasma arc welding. The method comprises: acquiring an image of the molten pool in a variable polarity plasma arc welding orifice; using a neural network model to predict the back wall angle of the molten pool in advance; deploying the neural network model in a computer, using the acquired image of the molten pool and the state of the molten pool as input, and the back wall angle of the molten pool as output; continuing welding if the predicted back wall angle of the molten pool is within a preset threshold range for the back wall angle of a standard molten pool; and rapidly feeding wire to the stagnation point on the back wall if the predicted back wall angle is outside the preset threshold range for the back wall angle of a standard molten pool, and immediately stopping the rapid wire feeding to the stagnation point on the back wall if the predicted back wall angle is within the threshold range for the back wall angle of a standard molten pool.

[0005] The present invention provides a method for predicting and controlling the state of the molten pool during continuous position change in variable polarity plasma arc welding, characterized in that: the neural network model is a convolutional neural network (CNN) and a long short-term memory neural network (LSTM); the CNN contains four convolutional layers to extract spatial feature information; and the LSTM serves as a temporal information extraction module for the neural network model.

[0006] The present invention provides a method for predicting and controlling the state of the molten pool during continuous position change in variable polarity plasma arc welding, characterized in that: the convolutional neural network can be replaced by VGG, Inception or ResNet neural network; the long short-term memory neural network LSTM can be replaced by GRU or seq2seq neural network.

[0007] According to the present invention, a method for predicting and controlling the state of the molten pool during continuous position change in variable polarity plasma arc welding is provided, characterized in that the state of the pinhole molten pool includes the longitudinal length of the pinhole molten pool and the included angle of the pinhole molten pool's rear wall; before the pinhole molten pool becomes unstable, the longitudinal length of the pinhole molten pool will increase.

[0008] According to the present invention, a method for predicting and controlling the state of the molten pool during continuous position change in variable polarity plasma arc welding is characterized by comprising: a threshold value of 85° to 90° for the included angle of the back wall of the pinhole molten pool; if the predicted included angle of the back wall of the pinhole molten pool is between 60° and 85°, the pinhole molten pool is in a state of not being cut and about to be cut, and wire feeding is performed at a speed higher than 100 cm / min; if the predicted included angle of the back wall of the pinhole molten pool is below 60°, the pinhole molten pool is in a cutting state, and wire feeding is performed at a speed higher than 120 cm / min; the stagnation point on the back wall surface is a point of abrupt change in back wall surface flow and morphology.

[0009] This invention also provides a control device for predicting and controlling the molten pool state during continuous position change in variable polarity plasma arc welding as described above. The device comprises: a welding system including a welding torch and a welding power source; a gas supply system for supplying gas to the welding torch; a camera monitoring system for acquiring images of the pinhole molten pool, the camera monitoring system facing the rear wall of the pinhole molten pool on the workpiece; an external rapid mass transfer system for rapidly feeding wire to the welding torch; and a control system connected to the welding system, the camera monitoring system, and the external rapid mass transfer system. The control system is used to predict the included angle of the pinhole molten pool rear wall based on the pinhole molten pool image acquired by the camera monitoring system and compare it with a preset standard pinhole molten pool rear wall angle threshold, thereby controlling the external rapid mass transfer system to rapidly feed wire to the stagnation point on the rear wall.

[0010] According to the present invention, a predictive control device for molten pool state during continuous variable position plasma arc welding is provided, characterized in that the welding system further includes: a wire feeding mechanism connected to the welding torch; the wire feeding mechanism is used to feed welding wire.

[0011] According to the present invention, a predictive control device for molten pool state during continuous position change in variable polarity plasma arc welding is provided, characterized in that the control system comprises: a computer connected to the camera monitoring system; a host computer connected to the computer; a processing unit connected to the host computer; and a control unit connected to the processing unit and the external rapid mass transfer system.

[0012] The method for predicting and controlling the state of the molten pool during continuous position change in variable polarity plasma arc welding provided in this invention uses a camera monitoring system and a control system to acquire the state of the pinhole molten pool during welding and predict the back wall angle of the pinhole molten pool in advance. The prediction angle is compared with a preset standard pinhole molten pool back wall angle threshold. When the predicted pinhole molten pool back wall angle exceeds the corresponding threshold range, the control system adjusts the external rapid mass transfer system to feed the wire rapidly, thereby keeping the pinhole molten pool back wall angle within the corresponding threshold range, thus curbing the instability of the pinhole molten pool and ensuring good weld formation. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Other features, objects, and advantages of this invention will become more apparent by reading the detailed description of the non-limiting embodiments with reference to the following drawings:

[0014] Figure 1 This is a flowchart of a method for predicting the state of the molten pool during continuous position changes in variable polarity plasma arc welding, provided in an embodiment of the present invention.

[0015] Figure 2 This is a flowchart of a method for controlling the state of the molten pool during continuous position changes in variable polarity plasma arc welding, as provided in an embodiment of the present invention.

[0016] Figure 3 This is a schematic diagram of the time axis division in an embodiment of the present invention.

[0017] Figure 4 This is a schematic diagram of the control device for the state of the molten pool during continuous position change in variable polarity plasma arc welding provided in an embodiment of the present invention.

[0018] Figure 5 yes Figure 4 The diagram shows the structure of a small-hole molten pool.

[0019] Figure label:

[0020] 1: Plasma arc welding power source; 2: Shielding gas channel; 3: Tungsten electrode channel; 4: Ion gas channel; 5: Cooling copper nozzle channel; 6: Host computer; 7: Shielding gas cylinder; 8: Plasma gas cylinder; 9: Control unit; 10: Processing unit; 11: Camera monitoring system; 12: Computer; 13: Workpiece; 14: Plasma welding torch; 15: Welding wire; 16: External rapid mass transfer system; 17: Back wall of small hole molten pool; 18: Back wall surface anchor point. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. The following embodiments will help those skilled in the art to further understand this invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of this invention. These all fall within the protection scope of this invention.

[0022] The following is combined Figure 1-5 This invention describes a method for predicting and controlling the state of the molten pool during continuous position changes in variable polarity plasma arc welding.

[0023] like Figure 1 As shown in the embodiment of the present invention, the method for predicting the state of the molten pool during continuous position change in variable polarity plasma arc welding includes: acquiring an image of the molten pool in the pinhole of the variable polarity plasma arc welding, and using a neural network model to predict the back wall angle of the pinhole molten pool in advance; deploying the neural network model in a computer 12, using the acquired pinhole molten pool image as input and the back wall angle of the pinhole molten pool as output.

[0024] Specifically, the camera monitoring system 11 acquires images of the molten pool in the small hole of the variable polarity plasma arc welding, then normalizes the images to a uniform size, arranges the images in time sequence, and inputs them into the neural network model.

[0025] Furthermore, in this embodiment of the invention, the neural network model is a convolutional neural network + long short-term memory neural network (CNN+LSTM), and the neural network is based on the Anaconda environment and the PyTorch framework. The convolutional neural network has 4 convolutional layers, no pooling layers, and fully connected layers. In the 4th layer, the 256×256 matrix is ​​transformed into a 1×1024 matrix and then passed to the long short-term memory neural network.

[0026] Furthermore, in this embodiment of the invention, the prediction time for the included angle of the back wall of the small-hole molten pool is approximately 1.5s to 2s.

[0027] like Figure 3As shown in the embodiments of the present invention, the method for predicting the state of the molten pool during continuous position change in variable polarity plasma arc welding emphasizes the advance prediction of the state of the pinhole molten pool, and rapidly feeds the wire at the stagnation point 18 on the rear wall of the pinhole molten pool before the pinhole molten pool becomes unstable, thereby suppressing the unstable state of the pinhole molten pool and maintaining a stable state.

[0028] like Figure 4 As shown in the embodiment of the present invention, the control device for the molten pool state during continuous position change in variable polarity plasma arc welding includes: a welding system, a gas supply system, a camera monitoring system 11, an external mass transfer system, and a control system. The welding system includes a welding torch 14 and a welding power source 1, and the gas supply system is used to supply gas to the welding torch. The camera monitoring system 11 is coaxially fixed with the plasma welding torch 1 so that the camera monitoring system 11 faces the rear wall 17 of the pinhole molten pool on the workpiece 13. The control system is connected to the camera monitoring system 11 and the external rapid mass transfer system. The control system is used to compare the included angle of the pinhole molten pool rear wall obtained by the camera monitoring system 11 with a preset standard pinhole molten pool rear wall included angle threshold, and then control the rapid wire feeding of the external rapid mass transfer system.

[0029] Specifically, the welding power source 1 provides current to the welding torch 14, and the gas supply system provides plasma gas and shielding gas to the welding torch 14. Before welding the metal, the camera monitoring system is positioned towards the back wall of the pinhole molten pool on the workpiece 13. Then, the arc of the welding torch 14 penetrates the workpiece 13, forming a pinhole molten pool on the workpiece 13. The camera monitoring system acquires the image and state of the pinhole molten pool, and then sends the predicted data to the control system. The control system compares the predicted pinhole molten pool back wall angle threshold with the preset standard pinhole molten pool back wall angle threshold. When the predicted pinhole molten pool back wall angle threshold is within the threshold range, the welding torch 14 continues welding. When the predicted pinhole molten pool back wall angle threshold is outside the range, the control system adjusts the external rapid mass transfer system to rapidly feed the wire at the pinhole molten pool back wall angle 18, so that the pinhole molten pool detected by the camera monitoring system is in a stable state and the pinhole molten pool back wall angle predicted by the computer 12 is within the standard pinhole molten pool back wall angle threshold range.

[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for predicting and controlling the state of the molten pool during continuous position changes in variable polarity plasma arc welding, characterized in that, include: A pinhole weld pool image of variable polarity plasma arc welding is acquired, and the back wall angle of the pinhole weld pool is predicted in advance using a neural network model. The neural network model is deployed in a computer, and the acquired pinhole weld pool image and pinhole weld pool status are used as inputs, while the back wall angle of the pinhole weld pool is used as the output. If the predicted back wall angle of the pinhole weld pool is within the preset threshold range of the standard pinhole weld pool back wall angle, welding continues. If the predicted back wall angle of the pinhole weld pool is outside the preset threshold range of the standard pinhole weld pool back wall angle, wire feeding is rapidly initiated at the back wall stagnation point. If the predicted back wall angle of the pinhole weld pool is within the threshold range of the standard pinhole weld pool back wall angle, the rapid wire feeding at the back wall stagnation point is immediately stopped. The neural network model consists of a Convolutional Neural Network (CNN) and a Long Short-Term Memory (LSTM) Neural Network. The CNN contains four convolutional layers to extract spatial feature information. The LSTM serves as the temporal information extraction module of the neural network model.

2. The method for predicting and controlling the molten pool state during continuous position variation in variable polarity plasma arc welding according to claim 1, characterized in that, include: The convolutional neural network can be replaced by VGG, Inception, or ResNet neural networks; the long short-term memory neural network LSTM can be replaced by GRU or seq2seq neural networks.

3. The method for predicting and controlling the molten pool state during continuous position variation in variable polarity plasma arc welding according to claim 1, characterized in that, The state of the small-hole molten pool includes the longitudinal length of the small-hole molten pool and the included angle of the rear wall of the small-hole molten pool; before the small-hole molten pool becomes unstable, the longitudinal length of the small-hole molten pool will increase.

4. The method for predicting and controlling the molten pool state during continuous position variation in variable polarity plasma arc welding according to claim 1, characterized in that, include: The threshold value for the included angle of the back wall of the small-hole molten pool is 85°~90°; if the predicted included angle of the back wall of the small-hole molten pool is between 60° and 85°, the small-hole molten pool is in a state of not being cut and about to be cut, and the wire is fed at a speed higher than 100cm / min; if the predicted included angle of the back wall of the small-hole molten pool is below 60°, the small-hole molten pool is in a cutting state, and the wire is fed at a speed higher than 120cm / min; the stagnation point on the back wall surface is the point of abrupt change in the back wall surface flow and morphology.

5. A control device for predicting and controlling the molten pool state during continuous position change in variable polarity plasma arc welding according to any one of claims 1-4, characterized in that, include: The welding system includes a welding torch and a welding power source; a gas supply system for supplying gas to the welding torch; a camera monitoring system for acquiring images of the pinhole weld pool, the camera monitoring system being oriented towards the back wall of the pinhole weld pool on the workpiece; an external rapid mass transfer system for rapidly feeding wire to the welding torch; and a control system connected to the welding system, the camera monitoring system, and the external rapid mass transfer system, the control system being used to predict the included angle of the pinhole weld pool back wall based on the pinhole weld pool image acquired by the camera monitoring system and compare it with a preset standard pinhole weld pool back wall angle threshold, thereby controlling the external rapid mass transfer system to rapidly feed wire to the stagnation point on the back wall.

6. The molten pool state prediction and control device for continuous position change during variable polarity plasma arc welding according to claim 5, characterized in that, The welding system further includes a wire feeding mechanism connected to the welding torch; the wire feeding mechanism is used to feed the welding wire.

7. The molten pool state prediction and control device for continuous variable position plasma arc welding according to claim 5, characterized in that, The control system includes: a computer connected to the camera monitoring system; a host computer connected to the computer; a processing unit connected to the host computer; and a control unit connected to the processing unit and the external rapid mass transfer system.

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