Self-adaptive powder spraying method based on multiple nozzles

Abstract

The invention relates to the technical field of powder spraying, in particular to a self-adaptive powder spraying method based on multiple nozzles, which comprises the following steps: judging whether the powder deposition rate is within a preset deposition rate range after spraying under the current powder performance and the initial nozzle height; spraying is conducted according to the initial nozzle height, whether the actual flow demand adjusting value exceeds the electrostatic adsorption capacity or not is predicted, and the initial nozzle voltage is increased for compensation; predicting whether the thickness uniformity of the coating after flow adjustment exceeds a fluctuation range or not, and adjusting the initial distance and the initial moving speed of adjacent nozzles; determining whether the current adjacent distance can cause electric field superposition or not, and determining whether to start an auxiliary nozzle to apply reverse bias voltage to perform auxiliary nozzle cooperative control or not; and whether the optimization degree of the powder deposition rate meets the expectation or not is determined, and the judgment standard of the predicted powder deposition rate is correspondingly adjusted. Spraying parameters are adaptively adjusted according to the complex condition of the surface of the component and powder characteristics, and the coating uniformity and quality stability are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of powder spraying technology, in particular to a self-adaptive powder spraying method based on multiple nozzles. BACKGROUND

[0002] Powder spraying technology is an advanced process for coating and forming a coating film in powder form, which has been widely used in modern industry due to its environmental protection, high efficiency and excellent coating film performance. The core of the technology is to use the principle of electrostatic adsorption and high temperature curing to adsorb to the surface of the grounded workpiece under the action of the electrostatic field, to uniformly coat the powder coating on the surface of the workpiece. The powder after spraying is melted and leveled under high temperature baking to form a dense and durable coating, and the un-deposited powder is recycled by a recycling system.

[0003] Chinese Patent Publication No. CN104588226A discloses a linear source electrode electrostatic powder spraying device, which includes a spraying device body, 2-100 powder pipe joints and a compressed air pipe joint located between each powder pipe joint are installed on the spraying device body, and a nozzle with a spray gap structure is located below the spraying cavity of the spraying device body, and an electrode is located below the nozzle. The invention uses a straight and slender gap instead of multiple spray guns arranged side by side at a certain distance, which can uniformly spray powder on the surface of the plate and high-speed electrostatic powder spraying. As can be seen, the linear source electrode electrostatic powder spraying device has the following problems: It cannot adaptively adjust the powder spraying method according to the complex surface of the part and the state of the powder, resulting in insufficient uniformity and quality stability of the coating. SUMMARY

[0004] Therefore, the present application provides a self-adaptive powder spraying method based on multiple nozzles to overcome the problem that the prior art cannot adaptively adjust the powder spraying method according to the complex surface of the part and the state of the powder.

[0005] To achieve the above-mentioned purpose, the present application provides a self-adaptive powder spraying method based on multiple nozzles, comprising: determining the initial nozzle height according to the required film thickness change of the current workpiece to be sprayed, and predicting the powder deposition rate after spraying in combination with the powder performance characteristics; determining whether to correct the initial nozzle height or optimize the powder deposition rate after spraying under the current powder performance and initial nozzle height, and determining whether the powder deposition rate is within the preset deposition rate range; spraying according to the initial nozzle height, predicting the coating estimated film thickness under the current coating width and initial moving speed according to the film thickness change trend, and predicting the required adjustment value of the actual flow according to whether the coating estimated film thickness meets the film thickness requirement; determining whether the demand adjustment value exceeds the electrostatic adsorption capacity at the current powder resistance, adjusting according to the demand adjustment value, or modifying the demand adjustment value and increasing the initial spray head voltage to compensate for the demand adjustment value; determining whether the coating thickness uniformity after adjusting the flow rate exceeds the fluctuation range according to the correspondence between the flow rate change and the center area film thickness of the nozzle, adjusting the initial spacing and the initial moving speed of the adjacent nozzles; determining whether the spray head angle needs to be adjusted by the rotating device according to the surface curvature of the curved surface transition area, and adjusting the initial spray head voltage of the nozzle according to the curved surface type of the curved surface transition area combined with the change amount of the spraying distance; determining whether the current adjacent spacing will cause electric field superposition according to the critical superposition spacing calculated based on the adjusted initial spray head voltage, and determining whether to start the auxiliary nozzle to apply a reverse bias for auxiliary nozzle cooperative control; reflecting the actual powder deposition rate after spraying by the powder recovery ratio, determining whether the optimization degree of the powder deposition rate meets the expectation, and adjusting the judgment standard of the powder prediction deposition rate accordingly.

[0006] Further, the process of determining whether the powder deposition rate is within the preset deposition rate range includes: determining the initial spray head height based on the film thickness-height theoretical model to determine the correspondence between the demand film thickness and the initial spray head height of different workpieces to be sprayed; taking the powder flowability as a powder performance characteristic, predicting the powder prediction deposition rate after spraying according to the powder performance characteristic and the determined initial spray head height; when the powder prediction deposition rate is greater than or equal to the first preset value, determining that the powder deposition rate under the current powder performance and initial spray head height exceeds the preset deposition rate range; when the powder prediction deposition rate is less than the first preset value and greater than or equal to the second preset value, determining that the powder deposition rate under the current powder performance and initial spray head height is within the preset deposition rate range; when the powder prediction deposition rate is less than the second preset value, determining that the powder deposition rate under the current powder performance and initial spray head height is lower than the preset deposition rate range.

[0007] Further, when the powder deposition rate exceeds the preset deposition rate range, powder spraying is performed according to the initial spray head height, when the powder deposition rate is within the preset deposition rate range, the powder deposition rate is further optimized, and when the powder deposition rate is lower than the preset deposition rate range, the initial spray head height is reduced according to the ratio of the powder prediction deposition rate to the first preset value.

[0008] Further, the process of determining whether the coating estimated film thickness meets the film thickness demand includes: Spraying according to the initial spray head height or the corrected initial spray head height, and measuring the actual film thickness of the initial spraying point in real time; According to the film thickness growth rate, predicting the coating estimated film thickness under the current coating width and the initial moving speed, and when the absolute value of the difference between the coating estimated film thickness and the required film thickness is greater than the difference evaluation value, judging that the coating estimated film thickness does not meet the film thickness requirement, and predicting the required adjustment value of the actual flow according to the coating estimated film thickness.

[0009] Further, the process of determining whether the required adjustment value exceeds the electrostatic adsorption capacity includes: According to the current actual flow and the current coating width, calculating the critical adsorption flow, and when the required flow is less than or equal to the critical adsorption flow, judging that the required adjustment value does not exceed the electrostatic adsorption capacity under the current powder resistance; When the required flow is greater than the critical adsorption flow, judging that the required adjustment value exceeds the electrostatic adsorption capacity under the current powder resistance, and reducing the required adjustment value and increasing the initial spray head voltage according to the required flow, the critical adsorption flow, and the safety factor.

[0010] Further, the process of predicting whether the coating thickness uniformity after the adjustment flow exceeds the fluctuation range includes: According to the corresponding relationship between the flow change and the center area film thickness of the nozzle, calculating the prediction ratio of the center area film thickness after the flow change to the initial center area film thickness; When the prediction ratio of the center area film thickness after the change to the initial center area film thickness is greater than the uniformity evaluation value, judging that the coating thickness uniformity after the adjustment flow exceeds the fluctuation range; According to the ratio of the uniformity evaluation value to the prediction ratio, reducing the initial spacing of the adjacent nozzles, and correspondingly increasing the initial moving speed.

[0011] Further, the process of adjusting the initial spray head voltage of the nozzle includes: when the actual change rate of the spraying distance is greater than the standard value, judging that there is a groove or a protrusion on the workpiece surface, and adjusting the initial spray head voltage according to the ratio of the change amount of the spraying distance to the average spraying distance.

[0012] Further, when the input surface curvature is less than or equal to a critical value, adjusting the spray head angle through the rotating device according to the surface curvature; when the surface curvature is greater than the critical value, adjusting the spray head angle through the rotating device according to the surface curvature, and correspondingly adjusting the initial spray head voltage according to the surface curvature.

[0013] Further, the process of determining whether the current adjacent spacing will cause electric field superposition includes: According to the adjusted initial spray head voltage, calculating the critical superposition spacing, and when the adjacent spacing of the current adjacent nozzles is less than or equal to the critical superposition spacing, judging that the current adjacent spacing will cause electric field superposition; The auxiliary nozzle is injected with reverse charged powder by the reverse bias applied by the reverse bias auxiliary electrode arranged above the superimposition area.

[0014] Further, the process of adjusting the determination criteria of the powder predicted deposition rate comprises: When the powder deposition rate is in the preset range or after the initial nozzle height is corrected, and the actual powder deposition rate is greater than or equal to the preset multiple of the powder predicted deposition rate, it is determined that the optimization degree of the powder deposition rate meets the expectation. When the powder deposition rate is in the preset range or after the initial nozzle height is corrected, and the actual powder deposition rate is less than the preset multiple of the powder predicted deposition rate, it is determined that the optimization degree of the powder deposition rate does not meet the expectation, and the ratio of the powder predicted deposition rate to the actual powder deposition rate is increased by the second preset value.

[0015] Compared with the prior art, the beneficial effects of the present application are that the multi-nozzle self-adaptive powder spraying method is an advanced surface treatment technology, which realizes uniform and efficient spraying on the surface of a complex workpiece by intelligently controlling the parameters and positions of multiple spraying nozzles. This method can automatically adjust the spraying mode according to the shape, size and surface features of the workpiece, improve the material utilization rate and spraying quality. Compared with paint spraying, powder spraying does not require the use of solvents, and the VOC (volatile organic compound) emission is zero, which is more environmentally friendly and can solve the problem of obvious color difference at the joint of a single nozzle. The powder spraying method of the present application optimizes the powder deposition rate (the weight percentage of the powder deposited on the surface of the workpiece in the total weight of the consumed powder during the spraying process) as much as possible, ensures that the spraying effect (coating thickness uniformity) of the workpiece after spraying meets the requirements, and overcomes the complex situation on the surface of the workpiece.

[0016] Further, since the powder deposition rate is affected by multiple factors, too long spraying distance (determined by a laser distance meter arranged on the nozzle) will cause the powder deposition rate to decrease, too high or too low nozzle voltage and air pressure, and different powder characteristics of the powder will all affect the deposition efficiency of the powder; the present application calculates the film thickness variation according to the required film thickness of the current workpiece to be sprayed to preliminarily determine the initial nozzle height, detects the flowability of the powder as a characteristic parameter to reflect the performance characteristics of the powder, and then predicts whether the powder deposition rate under the current powder flowability and nozzle height exceeds or is in the preset range according to the preliminarily determined initial nozzle height and the specific situation that the performance characteristics of the powder are in the standard range, accordingly corrects the preliminarily determined nozzle height, and further analyzes the working conditions of powder spraying for the current workpiece to be sprayed after the powder deposition rate is in the preset range or the nozzle height is corrected, and increases the adaptability of different demand parameters of the workpiece and different powder characteristics of the powder in the powder coating process.

[0017] Further, the determined or corrected height of the spray head is an important factor for the spraying distance and the coating width, the method predicts the estimated coating film thickness under the current coating width and the initial moving speed (the effective coating time of a point is determined by the current coating width and the initial moving speed) according to the film thickness change trend, calculates the required adjustment value of the actual flow, and since the powder charging is insufficient after the flow increases, the adsorption force will decrease, and the required adjustment value of the actual flow of the spray head under the current powder resistance is determined whether it will exceed the electrostatic adsorption capacity, the required adjustment value of the actual flow is corrected, and the Faraday cage effect is overcome by increasing the spray head voltage to compensate for the change in the required adjustment value, the film thickness is increased by increasing the adsorption amount on the workpiece surface without affecting the flow, the penetration of the difficult spraying area such as the groove and the acute angle is enhanced, and the edge leakage is reduced to improve the edge coverage.

[0018] Further, the conical region formed when the nozzle sprays powder has the characteristics of thick in the center and thin at the edge, the method eliminates the "saddle-shaped" thickness distribution of a single nozzle by overlapping the spraying regions of adjacent nozzles; at the same time, since the thick-thin characteristics of the conical region are related to the actual flow of the nozzle, the method judges the intensification of the thick-thin characteristics after adjusting the flow according to the predicted ratio, determines the influence degree on the uniformity of the coating thickness, and adjusts the initial spacing of adjacent nozzles to change the overlap ratio of the spraying regions of adjacent nozzles to avoid uneven thickness distribution caused by flow changes; and the flow change will affect the corresponding increase or decrease of the sprayed film thickness, the method adjusts the initial moving speed of the nozzle spraying to change the effective spraying time to reduce the influence of the change of the effective spraying amount on the sprayed film thickness, and increases the accuracy and stability of the adaptive adjustment process.

[0019] Further, for the grooves and protrusions on the workpiece surface, the method compensates for the reduced powder adsorption of the difficult-to-penetrate grooves by adjusting the spray head voltage, reduces the increased powder adsorption of the protrusions, and dynamically compensates for the input curved surface transition zone according to the curved surface type (concave, convex), adjusts the spray head angle through the rotating device of the spraying device according to the surface curvature to track the workpiece surface normal in real time, reduces the influence of the concave-convex curved surface transition zone on the thickness uniformity of the surface spraying, increases the consistency of the sprayed film thickness on the workpiece surface, and improves the adaptability to complex workpiece surfaces.

[0020] Further, since the adjacent spacing and the initial spray head voltage of adjacent nozzles are adjusted, and the electric field superposition will cause coating thickness fluctuation when the nozzle spacing is less than the critical superposition spacing, the method calculates the critical superposition spacing in real time after the parameters are adjusted, determines whether the current adjacent spacing will cause electric field superposition and thus thickness fluctuation according to the current spacing of adjacent nozzles and the calculated critical superposition spacing, and effectively compensates for the electric field superposition effect through the coordinated control of the reverse bias auxiliary electrode and the auxiliary nozzle to reduce the film thickness unevenness caused by the electric field superposition.

[0021] Further, the powder deposition rate is a key indicator in the powder spraying process, and by optimizing the powder performance, spraying process parameters and equipment conditions, the deposition rate can be effectively improved, thereby reducing material waste and improving production efficiency. The powder recovery ratio reflects the powder deposition rate condition of the spraying process, and when the optimization degree of the powder deposition rate does not meet the expectation, the determination standard of the powder predicted deposition rate is adjusted, the determination interval of the preliminary determined nozzle height is increased, the optimization degree of the adaptive adjustment of the multi-nozzle powder spraying method is increased, a closed loop is formed, and the response speed to abnormal conditions is improved when the powder recovery ratio abnormally increases. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A flowchart of the method of adaptive powder spraying based on multiple nozzles in the embodiments of the present application; Figure 2 A structural schematic diagram of the multi-nozzle spraying device in the embodiments of the present application; Figure 3 A spraying schematic diagram of the multi-nozzle spraying device in the embodiments of the present application; Figure 4 A flowchart of determining whether the powder deposition rate is within the preset deposition rate range according to the powder predicted deposition rate in the embodiments of the present application; Figure 5 A schematic diagram of the curved surface type of the curved surface transition area of the workpiece surface of the workpiece to be sprayed in the embodiments of the present application; In the figure: 1-nozzle, 2-workpiece, 3-assistant nozzle, 4-rotary device. DETAILED DESCRIPTION

[0023] In order to make the purpose and advantages of the present application clearer and more apparent, the present application will be further described below in conjunction with the embodiments; it should be understood that the specific embodiments described herein are only used to explain the present application, and do not limit the present application.

[0024] The preferred embodiments of the present application will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present application, and are not intended to limit the protection scope of the present application.

[0025] It should be noted that in the description of the present application, the terms "upper", "lower", "left", "right", "inner", "outer" and the like indicate the direction or positional relationship of the terms based on the direction or positional relationship shown in the drawings, which is only for the convenience of description, and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation, therefore it cannot be understood as a limitation of the present application.

[0026] Moreover, it needs to be explained that in the description of the present application, unless explicitly defined and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected, it can be mechanical connection, or electrical connection, it can be directly connected, or indirectly connected through intermediate medium, it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0027] Please refer to Figures 1-5 as shown, Figure 1 A method flow chart of adaptive powder spraying based on multiple nozzles in the embodiment of the present application; Figure 2 A structural schematic diagram of a multiple nozzle spraying device in the embodiment of the present application; Figure 3 A spraying schematic diagram of a multiple nozzle spraying device in the embodiment of the present application; Figure 4 A flow chart of determining whether the powder deposition rate is in the preset deposition rate range according to the powder predicted deposition rate in the embodiment of the present application; Figure 5 A curve type schematic diagram of a curved surface transition area of a workpiece surface of a workpiece to be sprayed in the embodiment of the present application.

[0028] The present application provides a kind of adaptive powder spraying method based on multiple nozzles, comprising: Step S1, according to the demand film thickness of current workpiece to be sprayed, calculate the film thickness change to determine the initial nozzle height, according to the powder performance characteristics and the initial nozzle height determined, predict the powder predicted deposition rate after spraying; Step S2, according to the powder predicted deposition rate, judge whether the powder deposition rate is in the preset deposition rate range after spraying under the current powder performance and the initial nozzle height, determine whether to correct the initial nozzle height or optimize the powder predicted deposition rate; Step S3, according to initial nozzle height, carry out spraying, according to the film thickness change trend, predict the coating estimated film thickness under the current coating width and initial moving speed, according to whether the coating estimated film thickness meets the film thickness demand, predict the demand adjustment value of actual flow; Step S4, determine whether the demand adjustment value of actual flow of nozzle under the current powder resistance will exceed the electrostatic adsorption capacity, adjust according to the demand adjustment value, or, correct the demand adjustment value and increase the initial nozzle voltage to compensate the demand adjustment value; Step S5, according to the corresponding relationship between flow change and center area film thickness of nozzle, predict whether the coating thickness uniformity after adjusting flow exceeds the fluctuation range, adjust the initial spacing and initial moving speed of adjacent nozzles; Step S6: Determine whether the nozzle angle needs to be adjusted by the rotating device based on the surface curvature of the curved transition zone, and adjust the initial nozzle voltage based on the surface type of the curved transition zone and the change in spraying distance. Step S7: Calculate the critical superposition spacing based on the adjusted initial nozzle voltage to determine whether the current adjacent spacing will lead to electric field superposition, and determine whether to start the auxiliary nozzle to apply reverse bias voltage for auxiliary nozzle cooperative control. Step S8: The actual powder deposition rate after spraying is reflected by the powder recovery ratio. It is determined whether the optimization degree of the powder deposition rate meets the expectations, and the judgment criteria of the predicted powder deposition rate are adjusted accordingly. Step S9: After spraying, perform high-temperature curing.

[0029] Multi-nozzle adaptive powder coating is an advanced surface treatment technology that achieves uniform and efficient coating of complex workpiece surfaces by intelligently controlling the parameters and positions of multiple spray nozzles. This method can automatically adjust the spraying pattern according to the workpiece's shape, size, and surface characteristics, improving material utilization and coating quality.

[0030] Specifically, compared to spray painting, powder coating eliminates the need for solvents, produces zero VOC (volatile organic compound) emissions, and is more environmentally friendly. It also addresses the issue of noticeable color differences at the seams of single-nozzle applications. The powder coating method of this invention optimizes the powder deposition rate (the percentage of powder weight deposited on the workpiece surface during the coating process relative to the total weight of powder consumed) as much as possible, while ensuring that the coating effect (coating thickness uniformity) meets requirements and simultaneously overcomes the complexities of the workpiece surface.

[0031] In the application scenario of this embodiment, the spraying device is equipped with several nozzles 1. After changing the workpiece 2 to be sprayed, the initial spraying distance between the several nozzles 1 and the surface of the workpiece 2 to be sprayed changes. Multi-nozzle adaptive spraying occurs in the spraying chamber, and a powder recovery device is provided in the spraying chamber to recover powder (powder recovery ratio).

[0032] In the powder coating process of this embodiment, several nozzles extend and retract away from the rotating device 4, thereby continuously coating the surfaces of different workpieces to be coated with powder during the continuous movement.

[0033] The initial nozzle height is determined by calculating the film thickness variation based on the required film thickness H of the workpiece to be coated, and the correspondence between the required film thickness and the initial nozzle height for different workpieces to be coated is determined based on the film thickness-height theoretical model. The theoretical model for film thickness-height is h = k·Q·η·t / [A·(d+α)] 2, wherein h is the current film thickness, Q is the powder flow rate, t is the effective spraying time, A is the effective spraying area, η is the deposition efficiency, d is the current spray head height, a is the powder diffusion coefficient, and k is the material constant.

[0034] In an embodiment, h, d, H, and D are in mm.

[0035] The initial spray head height after replacing the workpiece to be sprayed is determined according to the type of powder filled in the spraying device , and in an embodiment, the powder diffusion coefficient a is 10 mm. Specifically, the type of powder includes epoxy powder and metal powder, and in the embodiment, the type of powder filled in the spraying device is metal powder, and the metal powder required by different workpieces to be sprayed is different.

[0036] Since the powder deposition rate is affected by many factors, it is necessary to ensure that the powder deposition rate is within an appropriate range to ensure the utilization rate of the powder. The powder flowability reflects the performance characteristics of the powder, and when the powder flowability is within a standard range, it is more suitable for spraying and has a higher deposition efficiency, and the standard range is 18-21 s / 50 g.

[0037] Specifically, the powder flowability after replacing the filled powder is detected in real time by the Hall flowmeter arranged in the spraying device, and the powder flowability is taken as the performance characteristics of the powder.

[0038] According to the air pressure in the current spraying chamber, the performance characteristics of the powder, and the determined initial spray head height, the predicted powder deposition rate after spraying is predicted. In an embodiment, the spraying device is arranged in the spraying chamber, and the air pressure in the spraying chamber remains unchanged during the spraying process. The predicted powder deposition rate = the reference deposition rate · [1-β·(powder flowability-19.5 2 / 2.5 2 ]·e -γ(D-d0) , wherein the powder flowability is the detection value of the Hall flowmeter, β is the flowability sensitivity coefficient, γ is the height attenuation coefficient, and d0 is the reference height corresponding to the reference deposition rate. In an embodiment, the reference deposition rate is 0.9, the flowability sensitivity coefficient of the metal powder is 0.25, the height attenuation coefficient is 0.012 mm -1 , and the reference height is 120 mm. The reference deposition rate can be increased to 0.92-0.95 for high-sphericity powder (such as gas-atomized powder) and needs to be reduced to 0.85-0.88 for irregular powder (such as water-atomized powder); the flowability sensitivity coefficient is negatively correlated with the particle size of the powder, and since the smaller the particle size of the powder, the more significant the influence of the flowability, the greater the particle size (μm) of the powder, the smaller the value of β. When the powder predicted deposition rate is greater than or equal to the first preset value, it is judged that the powder deposition rate under the current powder performance and the initial nozzle height is out of the preset deposition rate range; When the powder predicted deposition rate is less than the first preset value and greater than or equal to the second preset value, it is judged that the powder deposition rate under the current powder performance and the initial nozzle height is in the preset deposition rate range; When the powder predicted deposition rate is less than the second preset value, it is judged that the powder deposition rate under the current powder performance and the initial nozzle height is lower than the preset deposition rate range; Specifically, when the powder deposition rate is out of the preset deposition rate range, powder spraying is performed according to the initial nozzle height, when the powder deposition rate is in the preset deposition rate range, further analysis is performed on the powder deposition rate, and when the powder deposition rate is lower than the preset deposition rate range, the initial nozzle height is reduced according to the ratio of the powder predicted deposition rate to the first preset value. The first preset value is 90%, the second preset value is 80%, and the preset deposition rate range is 80%-90%.

[0039] Specifically, since the powder deposition rate is affected by multiple factors, too far spraying distance (determined by a laser distance meter arranged through the nozzle) will cause the powder deposition rate to decrease, too high or too low nozzle voltage and air pressure, and different powder characteristics of the powder will all affect the powder deposition efficiency; the initial nozzle height is preliminarily determined according to the required film thickness of the current workpiece to be sprayed, the flowability of the powder is detected as a characteristic parameter to reflect the powder performance characteristics, and then whether the powder deposition rate under the current powder flowability and nozzle height is out of or in the preset range is predicted according to the preliminarily determined initial nozzle height and the specific situation that the powder performance characteristics are in the standard range, the preliminarily determined nozzle height is corrected accordingly, and the working condition of powder spraying for the current workpiece to be sprayed is further analyzed after the powder deposition rate is in the preset range or the nozzle height is corrected, thereby increasing the adaptability of different demand parameters of the workpiece and different powder characteristics of the powder in the powder coating process.

[0040] The actual flow and the nozzle voltage jointly determine the coating film thickness, and adjusting the nozzle voltage can increase the film thickness (increase the adsorption amount) without affecting the flow; The working condition of powder spraying for the current workpiece to be sprayed is further analyzed after the powder deposition rate is in the preset range or the initial nozzle height is corrected; Spraying is performed according to the initial nozzle height or the corrected initial nozzle height, and the actual film thickness of the initial spraying point is measured in real time by a laser profiler; The coating estimated film thickness under the current coating width and the initial moving speed (the effective coating time length of a point determined by the current coating width and the initial moving speed) is predicted according to the film thickness change trend. Specifically, the film thickness growth rate is calculated according to the ratio of the actual film thickness to the unit time length, and the coating estimated film thickness = film thickness growth rate × current coating width ÷ initial moving speed. As shown in Figure 3 The current coating width L is negatively correlated with the initial nozzle height, and the initial moving speed is a preset value of the spraying device. The dashed line in the figure represents the workpiece to be sprayed under different initial nozzle heights. When the absolute value of the difference between the coating estimated film thickness and the required film thickness H is greater than the difference evaluation value, it is determined that the coating estimated film thickness does not meet the film thickness requirement, and the demand adjustment value of the actual flow rate is predicted according to the coating estimated film thickness. The demand adjustment value of the actual flow rate is calculated according to the actual film thickness and the required film thickness H, and it is determined whether the demand adjustment value of the actual flow rate of the nozzle under the current powder resistance will exceed the electrostatic adsorption capacity (the powder is insufficiently adsorbed under the decreased adsorption force after the flow rate increases). Specifically, the demand adjustment value = actual flow rate × difference absolute value ÷ required film thickness H × gain coefficient. In implementation, the gain coefficient is 1.2, and the demand flow rate = actual flow rate + demand adjustment value.

[0041] According to whether the demand adjustment value will exceed the electrostatic adsorption capacity, the demand adjustment value is adjusted, or the demand adjustment value is reduced, and the initial nozzle voltage is increased to compensate for the demand adjustment value. Wherein, the actual flow rate is the detection value of the flow rate sensor, and the difference evaluation value is 5 μm.

[0042] The critical adsorption flow rate is calculated as follows: critical adsorption flow rate = vacuum permittivity × maximum allowable electric field intensity 2 × powder cloud effective cross-sectional area ÷ (2 × powder charge density); In implementation, the current is collected by a Faraday cup, the powder charge density is the ratio of the collected current to the current actual flow rate, the vacuum permittivity is 8.85 × 10 -12 F / m, the maximum allowable electric field intensity is 4 × 10 6 V / m, and the powder cloud effective cross-sectional area is positively correlated with the current coating width L.

[0043] When the demand flow rate is less than or equal to the critical adsorption flow rate, it is determined that the demand adjustment value under the current powder resistance does not exceed the electrostatic adsorption capacity. When the demand flow rate is greater than the critical adsorption flow rate, it is determined that the demand adjustment value under the current powder resistance exceeds the electrostatic adsorption capacity, and the demand adjustment value is reduced and the initial nozzle voltage is increased. Specifically, the demand adjustment value is reduced based on the difference between the quotient of the critical adsorption flow rate and the safety factor 1.2 and the demand flow rate, and the initial nozzle voltage is increased based on the ratio of the demand flow rate to the demand flow rate after reducing the demand adjustment value.

[0044] During implementation, the safety factor can be adjusted according to requirements.

[0045] Specifically, the determined or corrected nozzle height is a crucial factor affecting the spraying distance and coating width. This method predicts the estimated coating thickness based on the film thickness variation trend at the current coating width and initial moving speed (the current coating width and initial moving speed determine the effective coating time at a point). It calculates the actual flow rate adjustment value and, since the powder's insufficient charge and adsorption force will decrease after the flow rate increases, it determines whether the actual flow rate adjustment value of the nozzle will exceed the electrostatic adsorption capacity under the current powder resistance. It then corrects the actual flow rate adjustment value and compensates for the change in the adjustment value by increasing the nozzle voltage to overcome the Faraday cage effect. Without affecting the flow rate, it increases the film thickness by increasing the adsorption on the workpiece surface, enhancing the penetration of difficult-to-spray areas such as grooves and sharp corners, reducing edge missed spraying, and improving edge coverage.

[0046] In this embodiment, as Figure 3 As shown, the spraying areas of adjacent nozzles overlap by 20% to 30%.

[0047] The relationship between flow rate change and film thickness in the center region of the nozzle is: (demanded flow rate / actual flow rate). 流量影响指数 =Changed central region film thickness / Initial central region film thickness, calculate the predicted ratio of the central region film thickness after flow change to the initial central region film thickness based on the corresponding relationship; When the predicted ratio of the changed central region film thickness to the initial central region film thickness is greater than the uniformity evaluation value, it is determined that the coating thickness uniformity after adjusting the flow rate exceeds the fluctuation range, and the initial spacing and initial moving speed of adjacent nozzles are adjusted. Specifically, the initial spacing between adjacent nozzles is reduced based on the ratio of the uniformity evaluation value to the predicted ratio, and the initial moving speed is increased accordingly. In practice, the flow impact index is 0.9 and the uniformity evaluation value is 5%.

[0048] Specifically, the conical region formed when spraying powder from a nozzle exhibits a characteristic of being thicker at the center and thinner at the edges. This method eliminates the "saddle-shaped" thickness distribution of a single nozzle by overlapping the spraying areas of adjacent nozzles. Simultaneously, since the thickness characteristics of the conical region are related to the actual flow rate of the nozzle, this method judges the aggravation of the thickness characteristics after adjusting the flow rate based on the predicted ratio, determining the degree of influence on the coating thickness uniformity. By adjusting the initial spacing of adjacent nozzles, the overlap ratio of the spraying areas of adjacent nozzles is changed, thereby avoiding uneven thickness distribution caused by flow rate changes. Furthermore, flow rate changes affect the corresponding increase or decrease in the sprayed film thickness. This method reduces the impact of changes in the effective spraying amount on the sprayed film thickness by adjusting the initial moving speed of the nozzle spraying to change the effective spraying time, increasing the accuracy and stability of the adaptive adjustment process.

[0049] Among them, when the actual rate of change of the spraying distance measured by the laser rangefinder is greater than the standard value, it is determined that the spraying distance between the nozzle and the workpiece surface has increased sharply, and there are grooves or protrusions on the workpiece surface. The initial nozzle voltage is adjusted according to the ratio of the change in spraying distance to the average spraying distance. Specifically, the amount of powder adsorbed is reduced due to the difficulty in penetrating the groove by increasing the initial nozzle voltage, and the amount of powder adsorbed by the increased protrusion is reduced by decreasing the initial nozzle voltage. In practice, the actual rate of change of the spraying distance is the ratio of the change in spraying distance measured by the laser rangefinder to the unit time.

[0050] Simultaneously, dynamic electric field compensation is performed to adjust the initial nozzle voltage for the surface type (concave or convex) of the input curved transition zone; During implementation, the operator inputs the surface type and surface curvature of the transition zone of the workpiece to be sprayed before spraying.

[0051] Specifically, such as Figure 5 As shown, in this embodiment, the surface of the workpiece to be coated has a curved transition area, and the curved surface type of the curved transition area includes concave surface and convex surface; When the input surface curvature is less than or equal to the critical value, the nozzle angle is adjusted according to the surface curvature via the rotating device; when the surface curvature is greater than the critical value, the nozzle angle is adjusted according to the surface curvature via the rotating device, and the initial nozzle voltage is adjusted accordingly based on the surface curvature. Specifically, the normal to the workpiece surface is tracked in real time in the curved transition zone. The nozzle angle is adjusted by the rotating device according to the surface curvature. When the curved transition zone is concave, the nozzle angle is adjusted according to the surface curvature to increase the initial nozzle voltage. When the curved transition zone is convex, the nozzle angle is adjusted according to the surface curvature to decrease the initial nozzle voltage. The standard value is 15 mm / s, and the critical value is 0.5 mm. -1 .

[0052] It can be understood that the real-time tracking of the workpiece surface normal according to the adjustment of the spray head angle based on the workpiece surface curvature is a technical means that can be implemented by those skilled in the art according to the input workpiece surface data, and will not be described here.

[0053] Specifically, for the recesses and protrusions existing on the workpiece surface, the method compensates for the reduced powder adsorption amount of the recesses difficult to penetrate by adjusting the spray head voltage, reduces the increased powder adsorption amount of the protrusions, dynamically compensates for the surface type (concave, convex) of the input curved surface transition area, adjusts the spray head angle according to the surface curvature through the rotating device provided by the spraying device, and reduces the influence of the concave-convex curved surface transition area existing on the workpiece surface on the thickness uniformity of the surface spraying, increases the consistency of the spraying film thickness of the workpiece surface, and improves the adaptability to the complex workpiece surface.

[0054] According to the adjusted initial spray head voltage and other parameters, the critical superposition distance is calculated, and whether the current adjacent distance will cause electric field superposition and thus thickness fluctuation is determined according to the voltage polarity of the adjacent nozzle voltage and the critical superposition distance. In this embodiment, the voltage polarity of the adjacent nozzle voltage is the same, the electric field superposition is enhancement superposition, and the field strength increases after the electric field superposition.

[0055] The critical superposition distance = d , in the formula, is the vacuum dielectric constant, K is the powder characteristic constant, is the powder cloud mass density corresponding to the actual flow rate; In the implementation, the powder characteristic constant is 1.2×10 -8 C / kg, and the powder cloud mass density ranges from 0.05 to 0.15 kg / m³.

[0056] When the adjacent distance of the current adjacent nozzle is less than or equal to the critical superposition distance, it is determined that the current adjacent distance will cause electric field superposition, and the auxiliary nozzle 3 is started to apply a reverse bias for auxiliary nozzle cooperative control. The auxiliary nozzle is provided with a reverse bias auxiliary electrode, and the reverse bias is applied to the superposition area sprayed by the adjacent nozzle through the reverse bias auxiliary electrode, and auxiliary nozzle cooperative control is performed. The auxiliary nozzle is installed at the midpoint of the connecting line of the adjacent nozzles, and the reverse bias to be applied is =-k (the sum of the initial spray head voltages of the adjacent nozzles) / (2·e -d / λ ), in the formula, k is a compensation coefficient, d is the distance between the auxiliary electrode and the adjacent nozzle, and λ is an electric field attenuation constant. The auxiliary nozzle injects reverse-charged powder directly above the superposition area. In the implementation, the compensation coefficient is in the range of 0.3-0.6, the distance between the auxiliary electrode and the adjacent nozzle is half of the adjacent distance, and the electric field attenuation constant is in the range of 50-80 / mm.

[0057] Specifically, since the adjacent distance of the adjacent nozzles and the initial nozzle voltage are both adjusted, and the electric field superposition will cause the coating thickness to fluctuate when the nozzle distance is less than the critical superposition distance, the method calculates the critical superposition distance in real time after the parameters are adjusted, determines whether the current adjacent distance will cause the electric field superposition and thus cause the thickness fluctuation according to the current distance of the adjacent nozzles and the calculated critical superposition distance, effectively compensates the electric field superposition effect through the coordinated control of the reverse bias auxiliary electrode and the auxiliary nozzle, and reduces the film thickness unevenness problem caused by the electric field superposition.

[0058] As shown in Figure 3 The spraying device can adjust the powder output of the distributor to the nozzles, and adjust the actual flow of the nozzles through the valve opening degree arranged in the nozzles. In the implementation, the nozzle electrode is charged by a high-voltage electrostatic generator (60-100 kV), and the nozzle voltage of the nozzles can be adjusted.

[0059] The powder deposition rate after the adjustment parameters is reflected by the powder recovery ratio, and the actual powder deposition rate is calculated according to the powder recovery ratio, actual powder deposition rate=1-powder recovery ratio. When the powder deposition rate is in the preset range or after the initial nozzle height is corrected, and the actual powder deposition rate is greater than or equal to the preset multiple of the powder predicted deposition rate, it is judged that the optimization degree of the powder deposition rate meets the expectation. When the powder deposition rate is in the preset range or after the initial nozzle height is corrected, and the actual powder deposition rate is less than the preset multiple of the powder predicted deposition rate, it is judged that the optimization degree of the powder deposition rate does not meet the expectation, and the second preset value is increased according to the ratio of the powder predicted deposition rate to the actual powder deposition rate. In the implementation, the powder spraying device is arranged in the nozzle chamber, the powder recovery ratio is calculated by collecting the scattered powder in the nozzle chamber, the preset multiple is 1.2, and the implementation personnel can adjust the preset multiple according to the demand.

[0060] Specifically, the powder deposition rate is a key indicator in the powder spraying process, and by optimizing the powder performance, spraying process parameters and equipment conditions, the deposition rate can be effectively improved, thereby reducing material waste and improving production efficiency. The powder recovery ratio reflects the powder deposition rate condition of the spraying process, and when the optimization degree of the powder deposition rate does not meet the expectation, the determination standard of the powder predicted deposition rate is adjusted, the determination interval of the preliminary determined spray head height is increased, the optimization degree of the adaptive adjustment of the multi-nozzle powder spraying method is increased, a closed loop is formed, and the response speed to abnormal conditions is improved when the powder recovery ratio abnormally increases to reflect the increase of powder drift.

[0061] So far, the technical solutions of the present application have been described in combination with the preferred embodiments shown in the drawings, but those skilled in the art can easily understand that the protection scope of the present application is obviously not limited to these specific embodiments. Those skilled in the art can make equivalent changes or replacements to the related technical features without departing from the principles of the present application, and the technical solutions after the changes or replacements will fall within the protection scope of the present application.

[0062] The above description is only the preferred embodiments of the present application and is not intended to limit the present application; for those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. An adaptive powder coating method based on multiple nozzles, characterized in that, include: The initial nozzle height is determined based on the required film thickness variation of the workpiece to be coated, and the powder deposition rate is predicted after coating by combining the powder performance characteristics. Determine whether the powder deposition rate is within the preset deposition rate range after spraying under the current powder properties and initial nozzle height, and determine whether to correct the initial nozzle height or optimize the predicted powder deposition rate; Spraying is performed according to the initial nozzle height. The estimated coating thickness is predicted based on the coating thickness change trend at the current coating width and initial moving speed. Based on whether the estimated coating thickness meets the coating thickness requirement, the actual flow rate adjustment value is predicted. Determine whether the required adjustment value exceeds the electrostatic adsorption capacity under the current powder resistance, and adjust accordingly, or correct the required adjustment value and increase the initial nozzle voltage to compensate for the required adjustment value. Based on the correlation between the spray flow rate change and the film thickness in the center area of ​​the nozzle, predict whether the coating thickness uniformity after adjusting the flow rate exceeds the fluctuation range, and adjust the initial spacing and initial moving speed of adjacent nozzles. Determine whether the nozzle angle needs to be adjusted by rotating the device based on the surface curvature of the curved transition zone of the workpiece, and adjust the initial nozzle voltage according to the type of the curved transition zone and the change in spraying distance. Based on the adjusted initial nozzle voltage, the critical superposition spacing is calculated to determine whether the current adjacent spacing will lead to electric field superposition, and to determine whether to activate the auxiliary nozzle to apply reverse bias voltage for auxiliary nozzle cooperative control. The actual powder deposition rate after spraying is determined based on the powder recovery ratio, and the degree of optimization of the powder deposition rate is determined to meet expectations. The preset deposition rate range is then adjusted accordingly.

2. The adaptive powder coating method based on multiple nozzles according to claim 1, characterized in that, The process of determining whether the powder deposition rate is within the preset deposition rate range includes: The initial nozzle height is determined based on the correspondence between the required film thickness and the initial nozzle height for different workpieces to be coated, using the film thickness-height theoretical model. Using powder flowability as a powder performance characteristic, the predicted powder deposition rate after spraying is predicted based on the powder performance characteristics and the determined initial nozzle height. When the predicted powder deposition rate is greater than or equal to the first preset value, it is determined that the powder deposition rate of the coating under the current powder properties and initial nozzle height exceeds the preset deposition rate range. When the predicted powder deposition rate is less than a first preset value and greater than or equal to a second preset value, it is determined that the powder deposition rate of the coating under the current powder properties and initial nozzle height is within the preset deposition rate range. When the predicted powder deposition rate is less than the second preset value, it is determined that the powder deposition rate of the coating under the current powder properties and initial nozzle height is lower than the preset deposition rate range.

3. The adaptive powder coating method based on multiple nozzles according to claim 2, characterized in that, When the powder deposition rate exceeds the preset deposition rate range, powder coating is performed according to the initial nozzle height. When the powder deposition rate is within the preset deposition rate range, the powder deposition rate is optimized based on the film thickness variation trend analysis; When the powder deposition rate is lower than a preset deposition rate range, the initial nozzle height is reduced according to the ratio of the predicted powder deposition rate to the first preset value; The powder deposition rate being lower than the preset deposition rate range is the minimum value of the preset deposition rate range.

4. The adaptive powder coating method based on multiple nozzles according to claim 3, characterized in that, The process for determining whether the estimated coating thickness meets the film thickness requirements includes: Spraying is performed according to the initial nozzle height or the corrected initial nozzle height, and the actual film thickness at the initial spray point is measured in real time. Based on the film thickness growth rate, the estimated coating thickness is predicted under the current coating width and initial moving speed. When the absolute value of the difference between the estimated coating thickness and the required film thickness is greater than the difference evaluation value, it is determined that the estimated coating thickness does not meet the film thickness requirement. The actual flow rate adjustment value is then predicted based on the estimated coating thickness.

5. The adaptive powder coating method based on multiple nozzles according to claim 4, characterized in that, The process of determining whether the demand adjustment value will exceed the electrostatic adsorption capacity includes: The critical adsorption flow rate is calculated based on the current actual flow rate and the current coating width, where, When the required flow rate is less than or equal to the critical adsorption flow rate, it is determined that the required adjustment value does not exceed the electrostatic adsorption capacity under the current powder resistance. When the required flow rate is greater than the critical adsorption flow rate, it is determined that the required adjustment value exceeds the electrostatic adsorption capacity under the current powder resistance. Based on the required flow rate, the critical adsorption flow rate, and the safety factor, the required adjustment value is reduced and the initial nozzle voltage is increased.

6. The adaptive powder coating method based on multiple nozzles according to claim 5, characterized in that, The process of predicting whether the coating thickness uniformity after adjusting the flow rate exceeds the fluctuation range includes: The predicted ratio of the central region film thickness after the flow rate change to the initial central region film thickness is calculated based on the correspondence between the flow rate change and the film thickness in the central region of the nozzle. When the predicted ratio of the changed central region film thickness to the initial central region film thickness is greater than the uniformity evaluation value, it is determined that the coating thickness uniformity after adjusting the flow rate exceeds the fluctuation range. The initial spacing between adjacent nozzles is reduced based on the ratio of the uniformity evaluation value to the predicted ratio, and the initial moving speed is increased accordingly.

7. The adaptive powder coating method based on multiple nozzles according to claim 6, characterized in that, The process of adjusting the initial nozzle voltage includes determining whether there are grooves or protrusions on the workpiece surface when the actual rate of change of the spraying distance is greater than the standard value, and adjusting the initial nozzle voltage according to the ratio of the change in spraying distance to the average spraying distance.

8. The adaptive powder coating method based on multiple nozzles according to claim 7, characterized in that, When the surface curvature is less than or equal to a critical value, the nozzle angle is adjusted according to the surface curvature by the rotating device. When the surface curvature is greater than a critical value, the nozzle angle is adjusted according to the surface curvature by the rotating device, and the initial nozzle voltage is adjusted accordingly based on the surface curvature.

9. The adaptive powder coating method based on multiple nozzles according to claim 8, characterized in that, The process of determining whether the current adjacent spacing will lead to the superposition of electric fields includes: The critical superposition spacing is calculated based on the adjusted initial nozzle voltage. When the adjacent spacing of the current adjacent nozzles is less than or equal to the critical superposition spacing, it is determined that the current adjacent spacing will lead to electric field superposition. The auxiliary nozzle is activated to apply a reverse bias through the set reverse bias auxiliary electrode, and the auxiliary nozzle injects reverse-charged powder directly above the superposition area.

10. The adaptive powder coating method based on multiple nozzles according to claim 2, characterized in that, The process of adjusting the criteria for determining the powder prediction deposition rate includes: When the powder deposition rate is within a preset range or after initial nozzle height correction, and the actual powder deposition rate is greater than or equal to the predicted powder deposition rate by a preset multiple, it is determined that the degree of optimization of the powder deposition rate meets expectations. If the actual powder deposition rate is less than the predicted powder deposition rate by a preset multiple after the initial nozzle height correction is within the preset range, it is determined that the optimization degree of the powder deposition rate does not meet expectations, and the second preset value is increased according to the ratio of the predicted powder deposition rate to the actual powder deposition rate by a preset multiple.

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