Electrostatic field and ion wind based powder spreading compensation method and device for laser selective melting

Abstract

The application discloses a laser selective melting powder laying compensation method and device based on an electric field-ion wind. The powder laying operation is performed, and after the powder laying of a layer is completed, a current powder laying layer image is acquired; the current powder laying layer image is identified based on a powder laying layer image identification model, whether the current powder laying layer has impurities or defects is judged, if the current powder laying layer has impurities or defects, at least one of plasma wind or electric field is called to repair, then the identification, judgment or re-execution of the repair is repeated until the current powder laying layer meets the printing requirements. The application integrates the electric field and the plasma wind, and the two have a mutual promotion effect, can quickly remove the powder impurities and repair the powder defects in the laser selective melting powder laying process; breaks through the problem that the traditional powder laying layer defect repair method cannot be processed online, realizes high-precision non-damage online defect processing, and thus improves the powder laying quality of the laser selective melting.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and in particular to a laser selective melting powder spreading compensation method and apparatus based on electric field-ion wind. Background Technology

[0002] Additive manufacturing (AM) is a manufacturing method that uses 3D model data to process materials layer by layer to create shaped parts. This method, which does not require many processing tools, brings new design flexibility to the industry, reduces energy consumption, and shortens product time-to-market. Selective Laser Melting (SLM) is one of the most important processing methods in metal additive manufacturing. Its basic process is as follows: first, a layer of metal powder is laid on the substrate of the printing cavity; then, a high-energy-density laser is used to melt the selected area according to the slice data. After the laser scanning is completed, the powder cylinder platform is lowered to complete the next powder laying, and the laser scans the new layer of powder, repeating this process until printing is complete. The powder laying quality (density) significantly affects the powder's absorption rate of the laser. However, due to the van der Waals repulsion between powder particles and the influence of the high-speed flow field inside the printer cavity, the powder laying density is severely limited, thus affecting the quality of the printed sample. Therefore, improving existing powder laying devices to enhance the reliability of the powder laying process and improve the powder laying quality of selective laser melting is of great significance.

[0003] The powder spreading device is one of the key components of the laser selective melting equipment. The powder spreading device spreads powder onto the worktable through the mechanical movement of rollers or scrapers. However, due to the van der Waals repulsion between powders and the influence of the external flow field during the powder spreading process, the powder flows to both sides of the rollers or scrapers, and a large amount of powder is not spread onto the worktable, which seriously reduces the powder spreading efficiency and quality, and even contaminates the printer cavity. At present, the improvement of the powder spreading device for laser selective melting is mainly carried out in the following two aspects: (1) Improve the shape and structure of the powder spreading device. For example, patent CN110065233A designs an arc-shaped flexible scraper to adjust the fit between the flexible scraper and the powder spreading roller according to the actual situation and fills the groove on the inner side of the flexible scraper with rubber scraper strips to ensure that the fine powder on the powder spreading roller is effectively removed; patent CN106735213A provides an additive manufacturing powder spreading device with a flexible baffle, which can effectively prevent powder from leaking outside the forming area. However, this structural improvement relies heavily on experience-based design. For different printing cavities, auxiliary structures often need to be redesigned, resulting in poor consistency. In particular, it is difficult to effectively refine powder particles for agglomerated powders, making it difficult to guarantee powder spreading efficiency. (2) Improve the powder spreading method. For example, patent CN113102769A provides a composite additive manufacturing vibration powder spreading device that couples roller pressing technology to increase the compactness between powders. Patent CN113547743A provides an ultrasonic vibration powder spreading device to improve the density of the powder bed. While the powder spreading roller pushes the powder to spread evenly on the forming plane, the powder layer is compacted by vibration, making the powder layer more uniform, flat, and with a smoother and denser surface. However, these mechanical compaction methods are very likely to cause powder breakage, causing secondary damage to the powder spreading layer and failing to guarantee the repeatability and durability of the powder spreading quality. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a laser selective melting powder spreading compensation method based on electric field-ion wind, comprising,

[0005] Perform the powder spreading operation, and after the powder spreading of a certain layer is completed, obtain the image of the current powder spreading layer;

[0006] The current powder layer image is identified based on the powder layer image recognition model to determine whether there are impurities or defects in the current powder layer. If there are impurities or defects in the current powder layer, at least one of plasma wind or electric field is called for repair. Then the identification, judgment and repair are repeated or the repair is performed again until the current powder layer meets the printing requirements.

[0007] Furthermore, the step of repairing the current powder layer by invoking at least one of plasma wind or electric field if impurities or defects exist includes:

[0008] Preliminary experiments were conducted to obtain databases of powder materials manipulated by electric field and powder materials removed by ion wind. Based on the impurities or defects present in the current powder layer, repairs were made according to the aforementioned databases.

[0009] For impurities: particles smaller than 10 μm are removed by ion wind, and particles larger than 10 μm are removed by ion wind and then repaired by an electric field.

[0010] For defects: The electric field manipulates the powder to repair the defective area.

[0011] Furthermore, an ion air generator is installed in the powder hopper. Before the powder spreading operation, the powder in the powder hopper is fully stirred by the ion air generator installed in the powder hopper to prevent sticking.

[0012] Ionizing air guns are installed inside and outside the powder hopper. During powder spreading operations, the ionizing air guns are also used to blow away the powder flowing to both sides of the scraper.

[0013] Furthermore, the construction of the powder layer image recognition model includes,

[0014] Preliminary experiments were conducted to obtain image information of the current powder layer and divide it into training and test sets.

[0015] The test set is input into an embedded spiking neural network. The key regions are segmented using a PCNN network, features are extracted using an STN neural network, a function is introduced, and the weights are adjusted using the STDP algorithm to mask the multi-head attention layer to obtain a powder layer image recognition model.

[0016] Furthermore, before spreading the powder, a 3D model of the printed part is created, and the 3D model is processed in layers and a single-layer path is planned.

[0017] The present invention also provides a laser selective melting and powder spreading compensation device based on electric field-ion wind, including a printer cavity, a processor and a monitor, as well as a laser, a powder hopper, a scraper, a worktable and a robotic arm disposed in the printer cavity;

[0018] The robotic arm is equipped with an ion air gun and an electric field generator to provide plasma air and an electric field, respectively.

[0019] The powder hopper is used to transport the stored powder to the workbench;

[0020] The scraper is positioned above the workbench;

[0021] The monitor is used to acquire an image of the current powder layer after a certain powder layer has been laid and to transmit the image to the processor;

[0022] The processor stores a powder layer image recognition model, which is used to recognize the current powder layer image, determine whether there are impurities or defects in the current powder layer, and when there are impurities or defects in the current powder layer, call the robotic arm to repair it by at least one of plasma wind or electric field. The processor can repeatedly recognize, judge, or perform repair again until the current powder layer meets the printing requirements.

[0023] Furthermore, an ion wind generator is also installed inside the powder hopper.

[0024] Furthermore, the printer cavity is also provided with an air inlet and an air outlet, the air inlet being used to introduce protective gas, and the air outlet being used to discharge smoke and splashes.

[0025] Furthermore, the scraper is made of a flexible material.

[0026] This invention also provides the application of the above-described method in laser selective melting powder spreading printing.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] This invention integrates an electric field and plasma wind, which have a synergistic effect. It can rapidly remove impurities and repair defects in the powder layer during selective laser melting (SLM). An online monitoring system obtains the distribution of impurity particles and defects in the current powder layer, and then utilizes one or more of the plasma wind and electric fields to quickly address the defects. This directly addresses powder layer defects, overcoming the challenge of traditional powder layer defect repair methods being unable to process them online. It achieves high-precision, non-destructive online defect processing, thereby improving the powder layer quality of SLM. It can precisely and comprehensively enhance the density, uniformity, and flatness of the powder layer without introducing defects, greatly improving powder consistency, repeatability, and durability. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 A schematic diagram of a laser selective melting powder spreading compensation device based on electric field-ion wind is shown.

[0031] Figure 2 A flowchart is shown for laser selective melting and powder spreading printing using a laser selective melting and powder spreading compensation device based on electric field-ion wind.

[0032] Figure 3 A flowchart illustrating the construction of the powder layer image recognition model is shown;

[0033] Explanation of reference numerals in the attached figures:

[0034] 1. Printer cavity; 2. Scraper; 3. Toner hopper; 4. Ionizing air generator; 5. Toner bed; 6. Toner delivery pipe; 7. Fiber optic cable; 8. Monitor; 9. Ionizing air gun; 10. Electric field generator; 11. Processor; 12. Robotic arm; 13. Air inlet; 14. First recovery chamber; 15. Forming chamber; 16. Powder cylinder; 17. Second recovery chamber; 18. Air outlet; 19. Baffle. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Example

[0037] like Figure 1 As shown, a laser selective melting and powder spreading compensation device based on electric field-ion wind includes a printer cavity 1, a processor 11, and a monitor 8, as well as a laser, a powder hopper 3, a scraper 2, a worktable, and a robotic arm 12 disposed within the printer cavity 1; the scraper 2 is disposed above the powder bed 5 of the worktable; a baffle 19 is also disposed beside the scraper 2; a first recovery chamber 14, a forming chamber 15, a powder cylinder 16, and a second recovery chamber 17 are disposed below the worktable, and the first recovery chamber 14 and the second recovery chamber 17 are respectively connected to the forming chamber 15 and the powder cylinder 16 via flexible hoses; the robotic arm 12 is equipped with... The ion air gun 9 and the electric field generator 10 are used to provide plasma air and electric field, respectively; the monitor 8 is used to acquire the current powder layer image after a certain powder layer is laid and transmit the image to the processor 11; the processor 11 stores a powder layer image recognition model, which is used to identify the current powder layer image, determine whether there are impurities or defects in the current powder layer, and when there are impurities or defects in the current powder layer, call the robotic arm 12 to repair it by at least one of plasma air or electric field. The processor 11 can repeatedly identify, judge, or perform repair again until the current powder layer meets the printing requirements.

[0038] The printer cavity 1 has a window covered with transparent material at its upper end, through which the monitor 8 can observe the image of the printed parts inside the printer cavity 1. At least one air inlet 13 and one air outlet 18 are located on different sides of the printer cavity 1. The air inlet 13 continuously supplies protective gas, while the air outlet 18 removes fumes and splatter generated during processing. An ion air generator 4 is also installed inside the powder hopper 3. Before powder spreading, the ion air generator is activated to vibrate and sieve the powder particles, refining them and preventing them from sticking together. During powder spreading, the ion air generator blows away powder particles flowing to both sides of the scraper 2, preventing powder particles from collapsing due to intermolecular van der Waals forces. One outlet of the powder hopper 3 is connected to a powder delivery pipe 6. When powder needs to be used to repair the powder layer, the powder hopper 3 opens and outputs powder through the powder delivery pipe 6. Then, the robotic arm 12 moves the electric field generator 10 to attract the powder for repair.

[0039] In this embodiment, the processor 11 and the monitor 8 are connected by optical fiber 7; the monitor 8 and the powder hopper 3 are connected by optical fiber 7; the processor 11 is an industrial control computer; the monitor 8 is a CCD camera; the laser can provide laser with a wavelength of 200nm to 10.6μm; the scraper 2 is made of flexible material.

[0040] like Figure 2 As shown, a method for laser selective melting powder spreading printing using the above-described apparatus is also provided, comprising the following steps:

[0041] S1. Based on the laser selective melting system's dedicated layering software stored on the industrial control computer, a CAD 3D model of the printed part is established, and the CAD 3D model is layered and single-layer path planning is completed.

[0042] S2. Provide printing conditions: Use processor 11 to control the laser, preheat the printing area of ​​the worktable to 200-300°C, and introduce argon gas into the air inlet 13 as a protective gas during printing. Set the powder spreading speed to 30mm / s and the layer thickness to 30nm.

[0043] S3. Turn on the ion wind generator 4 to make the airflow velocity of the ion wind 0.3m / s, and fully stir the AlSi10Mg powder with a particle size of 20-50μm stored in the powder chamber to prevent it from sticking together.

[0044] S4. Open the powder hopper to deliver AlSi10Mg powder, start the scraper 2 to spread the powder at a speed of 30mm / s, and the robotic arm 12 controls the ion gun 9 to blow away the powder flowing to both sides of the scraper 2 to prevent the powder from collapsing due to intermolecular van der Waals forces.

[0045] S5. After a certain layer of powder is laid, the CCD camera acquires the image of the current powder layer and transmits the image to the industrial control computer. The industrial control computer quickly captures millisecond-level defect image information based on the stored powder layer image recognition model, and determines whether there are impurities or defects in the current powder layer. If there are impurities or defects in the current powder layer, based on the electric field-controlled powder database and the ion wind-blown powder database stored in the industrial control computer, and combined with the impurities or defects in the current powder layer, at least one of plasma wind or electric field is called for repair. Then the identification, judgment, or repair is performed again until the current powder layer meets the printing requirements.

[0046] Among them, such as Figure 3 As shown, the construction of the powder layer image recognition model includes: conducting pre-experiments, acquiring the current powder layer image information and dividing it into training and test sets, inputting the test set into an embedded spiking neural network, and, based on the PCNN network, quickly establishing a region of interest with a radius of 50 pixels in the original image, using the maximum inter-class variance method for binarization, directly mapping the centroid coordinates to adjacent layers, and automatically generating 2D seed points. Based on the STN neural network, features are extracted in one step, with a pulse time interval of 15, and a function function f(θ) is introduced to control the matrix scale. The ratio of the training set to the test set is selected as 7:3. Through the visualization of STDP, the synapses adjust the weights additionally through the learning rate Ap and Ad, and a masked multi-head attention layer is adopted. A mask matrix is ​​introduced between the query and the key, and the attention weights of all words after this position are set to negative infinity to ensure the autoregressive nature of the model.

[0047] The EDEM discrete element simulation software and Fluent fluid dynamics simulation software were coupled in two directions. The powder material adopted the JKR contact model, the collision recovery coefficient was set to 0.3, the friction coefficient was set to 0.7, and the plasma wind velocity, i.e. the initial flow field velocity, was set to 0.3 m / s.

[0048] Electrostatic stress on powder surface (ρ) s E n The expression is as follows:

[0049]

[0050] In the formula, ρ s For surface charge density, E n K is the normal electric field, α is the electric field enhancement coefficient, and K is the electric field enhancement coefficient. a ε represents the positive ion mobility. a σ is the dielectric constant of air. f ε is the dielectric conductivity of the fluid. f denoted as the dielectric constant of the dielectric fluid, V as the voltage, and d as the distance between the electrode and the powder bed.

[0051] Based on 100 sets of preliminary experiments on electric field-controlled powder and ion wind-blown powder, respectively, an electric field-controlled powder database and an ion wind-blown powder database were constructed. The electric field-controlled powder database includes the relationship between electric field strength, electrostatic stress on the powder surface, and powder silo density; the ion wind-blown powder database includes the relationship between ion wind rate and stratification density, etc.

[0052] For impurities: particles smaller than 10 μm are removed by ionizing air, and particles larger than 10 μm are removed by ionizing air and then repaired by an electric field.

[0053] For defects: the electric field controls the powder to repair the defective area. Powder spreading defects include insufficient powder, overlapping powder, etc.

[0054] S6. After the current powder layer meets the printing requirements, determine whether the workpiece has been printed. If the printing is completed, end the printing process; if not, repeat steps S4 and S5 until the printing is completed.

[0055] In summary, the laser selective melting powder spreading compensation method and device based on electric field-ion wind proposed in this invention can repair various powder spreading defects such as powder shortage and powder stacking with high precision in situ. In particular, it is of great significance for improving the quality of additive manufacturing products and promoting their industrial application, especially for powder spreading impurities of different sizes.

[0056] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. 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 selective melting powder spreading compensation method based on electric field-ion wind, characterized in that, include, Perform the powder spreading operation, and after the powder spreading of a certain layer is completed, obtain the image of the current powder spreading layer; The current powder layer image is identified based on the powder layer image recognition model to determine whether there are impurities or defects in the current powder layer. If there are impurities or defects in the current powder layer, at least one of ion wind or electric field is called for repair. Then the identification and judgment are repeated, or the repair is performed again, until the current powder layer meets the printing requirements. The step of repairing the current powder layer by invoking at least one of ion wind or electric field if impurities or defects exist includes: Preliminary experiments were conducted to obtain an electric field-controlled powder database and an ion wind-blown powder database. Based on the impurities or defects present in the current powder layer, repairs were made according to the electric field-controlled powder database and the ion wind-blown powder database. For impurities: particles smaller than 10 μm are removed by ion wind, and particles larger than 10 μm are removed by ion wind and then repaired by an electric field. For defects: the electric field manipulates the powder to repair the defective area; The construction of the powder layer image recognition model includes: Preliminary experiments were conducted to obtain image information of the current powder layer and divide it into training and test sets. The test set is input into an embedded spiking neural network. The key regions are segmented using a PCNN network, features are extracted using an STN neural network, a function is introduced, and the weights are adjusted using the STDP algorithm to mask the multi-head attention layer to obtain a powder layer image recognition model.

2. The laser selective melting powder spreading compensation method based on electric field-ion wind according to claim 1, characterized in that, An ion air generator is installed in the powder hopper. Before the powder spreading operation, the powder in the powder hopper is fully stirred by the ion air generator installed in the powder hopper to prevent sticking. Ionizing air guns are installed inside and outside the powder hopper. During powder spreading operations, the ionizing air guns are also used to blow away the powder flowing to both sides of the scraper.

3. The laser selective melting powder spreading compensation method based on electric field-ion wind according to claim 1, characterized in that, Before spreading the powder, a 3D model of the printed part is created, and the 3D model is processed into layers and a single-layer path is planned.

4. A laser selective melting powder spreading compensation device based on electric field-ion wind, used to perform the laser selective melting powder spreading compensation method based on electric field-ion wind as described in any one of claims 1-3, characterized in that, It includes the printer cavity, processor and monitor, as well as the laser, toner hopper, scraper, worktable and robotic arm set in the printer cavity; The powder hopper is used to transport the stored powder to the workbench; The scraper is positioned above the workbench; The robotic arm is equipped with an ion air gun and an electric field generator to provide ion air and an electric field, respectively. The monitor is used to acquire an image of the current powder layer after a certain powder layer has been laid and to transmit the image to the processor; The processor stores a powder layer image recognition model, which is used to recognize the current powder layer image, determine whether there are impurities or defects in the current powder layer, and when there are impurities or defects in the current powder layer, call the robotic arm to repair it by at least one of ion wind or electric field. The processor can repeatedly recognize, judge, or perform repair again until the current powder layer meets the printing requirements.

5. The laser selective melting powder spreading compensation device based on electric field-ion wind according to claim 4, characterized in that, An ion wind generator is also installed inside the powder hopper.

6. The laser selective melting powder spreading compensation device based on electric field-ion wind according to claim 4, characterized in that, The printer cavity is also provided with an air inlet and an air outlet. The air inlet is used to introduce protective gas, and the air outlet is used to discharge smoke and splashes.

7. The laser selective melting powder spreading compensation device based on electric field-ion wind according to claim 4, characterized in that, The scraper is made of a flexible material.

8. The application of the laser selective melting powder spreading compensation method based on electric field-ion wind as described in any one of claims 1 to 3 in laser selective melting powder spreading printing.

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