Selective melting light beam dynamic focusing and layered manufacturing cooperative control method and system

Abstract

The invention discloses a selective melting light beam dynamic focusing and layered manufacturing cooperative control method and system, and belongs to the field of selective melting additive manufacturing. The method comprises the steps of collecting feature data of a current forming layer; calling a hierarchical feature-focusing parameter mapping library constructed by off-line molten pool simulation; light beam focusing parameters are adjusted in real time; constructing'focusing-scanning-powder laying 'three-parameter closed-loop cooperative control, and synchronously adjusting the other two types if any parameter exceeds a threshold value; molten pool and contour data are collected, and parameters of the next layer are corrected when abnormity occurs. The system comprises a dynamic focusing module, a cooperative control module and a sensing feedback module, and can be additionally provided with a multi-beam cooperation and defect correction subunit. According to the method, focusing and layer feature adaptation are achieved, energy input is stabilized, forming defects are reduced, part performance is guaranteed, forming precision and efficiency are improved, and the method is adaptive to multi-material and complex structural parts.

Description

Technical Field

[0001] This invention relates to the field of selective melting additive manufacturing, and in particular to a method and system for the coordinated control of dynamic focusing of selective melting beam and layered manufacturing. Background Technology

[0002] In the high-end manufacturing sector, selective melting additive manufacturing technology, with its advantages of eliminating the need for molds and directly forming complex structural parts, has been widely applied in aerospace, medical devices, and precision machinery. Currently, the core development of this technology revolves around "improving forming accuracy" and "optimizing manufacturing processes." The industry generally adopts the core logic of layered manufacturing, which involves slicing the three-dimensional model of a part into two-dimensional layers and completing the forming process of powder spreading and beam scanning melting layer by layer. At the same time, beam focusing control is a key factor affecting forming quality, and related research focuses on optimizing focusing parameters and applying sensing technologies. For example, basic data is collected through laser displacement sensors, and the molten pool morphology is simulated using finite element simulation. Some equipment also introduces multi-beam forming schemes to improve the manufacturing efficiency of large-sized parts. The overall technology system is gradually improving towards automation and precision.

[0003] However, existing selective melting additive manufacturing technologies still have significant shortcomings in the coordinated control of beam focusing and layer manufacturing. Specific problems include: First, existing technologies often fail to collect real-time data on the actual layer characteristics of the current forming layer, such as actual layer thickness, contour curvature, and feature dimensions. This results in beam focusing parameters, such as focal length, spot diameter, and depth of focus, often using fixed values ​​or manually segmented settings, which cannot adapt to the geometric differences between different layers and makes it difficult to achieve precise matching between focusing parameters and layer features. Second, there is a lack of a pre-built "layer feature-focusing parameter mapping library," making it impossible to quickly access and match the current layer features using offline simulation results. The optimal focusing parameters for layer feature adaptation are inefficient and dependent on experience in the parameter determination process; third, the control logic of beam focusing, scanning path, and powder spreading speed are independent of each other and no closed-loop collaborative mechanism is built. When any parameter fluctuates due to external factors, the other two types of parameters cannot be adjusted synchronously, which can easily lead to unstable energy input per unit area; fourth, no real-time feedback correction mechanism for molten pool state and forming contour is established. Even if molten pool abnormalities or forming defects are detected, the focusing parameters and collaborative control thresholds of the next layer cannot be corrected in time, making it difficult to form a closed loop of quality control throughout the entire process, which ultimately affects the forming accuracy and performance stability of the parts. Summary of the Invention

[0004] The purpose of this invention is to overcome one or more shortcomings of the prior art and provide a method and system for coordinated control of dynamic focusing of selective melting beam and layered manufacturing.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for coordinated control of dynamic focusing of a selective melting beam and layered manufacturing includes the following steps:

[0007] S1. Collect the layer feature data of the current forming layer during the selected area melting and layering manufacturing process. The layer feature data includes at least the actual layer thickness, contour curvature, and feature dimensions.

[0008] S2. Call the pre-built "layered feature-focusing parameter mapping library". The mapping library establishes the correlation between different layer feature data and optimal focusing parameters through offline melt pool simulation. The optimal focusing parameters include at least focal length, spot diameter and depth of focus.

[0009] S3. Based on the layer feature data collected in step S1 and the mapping library called in step S2, the beam focusing parameters are adjusted in real time through the dynamic focusing actuator to achieve the adaptation of the current forming layer focusing parameters and layer features.

[0010] S4. Synchronously acquire scanning path signal, powder spreading speed signal and beam focusing parameter signal to construct a three-parameter closed-loop collaborative control logic of "focusing-scanning-powder spreading". When any parameter exceeds the preset threshold, the other two types of parameters are adjusted synchronously.

[0011] S5. Collect the melt pool status data and forming contour data of the current forming layer. If an abnormal melt pool or forming defect is detected, correct the focusing parameters and collaborative control threshold of the next layer in real time to form a closed-loop control.

[0012] Furthermore, when adjusting the beam focusing parameters in real time as described in step S3, the target focal length needs to be determined comprehensively by combining the reference focal length, the actual layer thickness, and the contour curvature: based on the reference focal length corresponding to a specific material, the focal length is adjusted according to the change in the actual layer thickness by using the layer thickness influence coefficient determined by the material's thermal conductivity; at the same time, the focal length is supplemented by adjusting the curvature influence coefficient determined by the contour forming accuracy requirements according to the change in the contour curvature radius, so that the focal length adapts to the geometric characteristics of the current layer.

[0013] Furthermore, in the "focus-scan-powder spreading" three-parameter closed-loop collaborative control logic described in step S4, the scanning speed and the spot diameter need to be adjusted in tandem: with the reference scanning speed and reference spot diameter corresponding to a specific material as a reference, when the spot diameter is adjusted according to the layer characteristics, the scanning speed needs to be adjusted synchronously to ensure that the beam energy input per unit area remains consistent, and to avoid over-melting or non-fusion due to changes in spot size.

[0014] Furthermore, when the selected area melting adopts multi-beam forming, step S4 also includes coordinated adjustment between beams: for edge beams, the focal length of the edge beam relative to the center beam needs to be adjusted according to the overlapping area of ​​the heat-affected zone of the adjacent beam molten pool and the heat-affected zone compensation coefficient determined by the material melting point, so as to reduce the thermal superposition deformation in the beam intersection area and avoid the formation of splicing seams.

[0015] Furthermore, the process of real-time correction of the focal length of the next layer if an abnormal molten pool temperature is detected in step S5 is as follows: when the actual temperature of the molten pool exceeds the preset optimal temperature range, the focal length of the next layer is reduced according to the temperature difference and the temperature compensation coefficient determined by the specific heat capacity of the material. By reducing the spot size, the local energy input is reduced, so that the molten pool temperature returns to the optimal range.

[0016] Furthermore, in step S4, when the powder spreading speed fluctuates, the focal length needs to be adjusted accordingly: with the reference powder spreading speed as a reference, calculate the deviation ratio between the real-time powder spreading speed and the reference powder spreading speed, and combine the powder spreading speed influence coefficient determined by the powder flowability to adjust the current focal length to ensure that the melt pool depth still meets the molding requirements when the powder spreading amount changes.

[0017] Furthermore, the specific process of detecting forming defects in step S5 includes: capturing the contour image of the current forming layer using a machine vision camera, extracting the contour edge coordinates using an edge detection algorithm, and calculating the deviation between the actual contour size and the design size; if the deviation is greater than a preset deviation threshold, it is determined to be a forming defect, and according to the defect type (collapsed edge, spheroidization, or lack of fusion), the corresponding correction parameters are called from the "Layer Feature-Focusing Parameter Mapping Library" to adjust the focal length and spot diameter of the next layer.

[0018] Furthermore, the construction process of the "layer feature-focusing parameter mapping library" mentioned in step S2 includes: for different materials to be formed, finite element simulation is used to simulate the molten pool morphology (molten pool depth, width and temperature field distribution) under different layer thicknesses and contour curvatures, and the focusing parameter combination that makes the molten pool morphology meet the forming requirements is selected, a one-to-one correspondence between layer feature data and focusing parameters is established, and stored in the database of the control unit; when the material to be formed is changed, the mapping library can be updated through offline simulation.

[0019] The beneficial effects of this invention are:

[0020] (1) Through the beam dynamic focusing technology driven by layer features, the focusing parameters are precisely matched with the geometric features of the forming layer, and the forming problem caused by traditional fixed parameters is solved.

[0021] (2) By using the three-parameter closed-loop collaborative control technology of "focusing-scanning-powder spreading", the effect of stable beam energy input per unit area and reduced inconsistency in intralayer fusion caused by fluctuation of a single parameter is achieved;

[0022] (3) By real-time feedback correction of the molten pool state and the forming contour and multi-beam collaborative technology, the effect of reducing the occurrence rate of forming defects and ensuring the stability of the mechanical properties of the parts can be achieved. Attached Figure Description

[0023] Figure 1 The flowchart illustrates the specific steps of a method for coordinated control of dynamic focusing of a selective melting beam and layered manufacturing, as provided in this embodiment. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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.

[0025] Example 1

[0026] See Figure 1 This embodiment provides a method for coordinated control of dynamic focusing of a selective melting beam and layered manufacturing, including the following steps:

[0027] S1. Collect the layer feature data of the current forming layer during the selected area melting and layering manufacturing process. The layer feature data includes at least the actual layer thickness, contour curvature, and feature dimensions.

[0028] S2. Call the pre-built "layered feature-focusing parameter mapping library". The mapping library establishes the correlation between different layer feature data and optimal focusing parameters through offline melt pool simulation. The optimal focusing parameters include at least focal length, spot diameter and depth of focus.

[0029] S3. Based on the layer feature data collected in step S1 and the mapping library called in step S2, the beam focusing parameters are adjusted in real time through the dynamic focusing actuator to achieve the adaptation of the current forming layer focusing parameters and layer features.

[0030] S4. Synchronously acquire scanning path signal, powder spreading speed signal and beam focusing parameter signal to construct a three-parameter closed-loop collaborative control logic of "focusing-scanning-powder spreading". When any parameter exceeds the preset threshold, the other two types of parameters are adjusted synchronously.

[0031] S5. Collect the melt pool status data and forming contour data of the current forming layer. If an abnormal melt pool or forming defect is detected, correct the focusing parameters and collaborative control threshold of the next layer in real time to form a closed-loop control.

[0032] When adjusting the beam focusing parameters in real time as described in step S3, the target focal length needs to be determined comprehensively by combining the reference focal length, the actual layer thickness, and the contour curvature: based on the reference focal length corresponding to a specific material, the focal length is adjusted according to the change in the actual layer thickness by using the layer thickness influence coefficient determined by the material's thermal conductivity; at the same time, the focal length is further adjusted according to the change in the contour curvature radius by using the curvature influence coefficient determined by the contour forming accuracy requirements, so that the focal length adapts to the geometric characteristics of the current layer.

[0033] In the "focus-scan-powder spreading" three-parameter closed-loop collaborative control logic described in step S4, the scanning speed and the spot diameter need to be adjusted in tandem: with the reference scanning speed and reference spot diameter corresponding to a specific material as a reference, when the spot diameter is adjusted according to the layer characteristics, the scanning speed needs to be adjusted synchronously to ensure that the beam energy input per unit area remains consistent, and to avoid over-melting or non-fusion due to changes in spot size.

[0034] When the selected area melting adopts multi-beam forming, step S4 also includes coordinated adjustment between beams: for edge beams, the focal length of the edge beam relative to the center beam needs to be adjusted according to the overlapping area of ​​the heat-affected zone of the adjacent beam molten pool and the heat-affected zone compensation coefficient determined by the melting point of the material, so as to reduce the thermal superposition deformation in the beam intersection area and avoid the formation of splicing seams.

[0035] The process of real-time correction of the focal length of the next layer if an abnormal molten pool temperature is detected in step S5 is as follows: when the actual temperature of the molten pool exceeds the preset optimal temperature range, the focal length of the next layer is reduced according to the temperature difference and the temperature compensation coefficient determined by the specific heat capacity of the material. By reducing the spot size, the local energy input is reduced, so that the molten pool temperature returns to the optimal range.

[0036] In step S4, when the powder spreading speed fluctuates, the focal length needs to be adjusted accordingly: using the reference powder spreading speed as a reference, calculate the deviation ratio between the real-time powder spreading speed and the reference powder spreading speed, and combine the powder spreading speed influence coefficient determined by the powder flowability to adjust the current focal length to ensure that the melt pool depth still meets the molding requirements when the powder spreading amount changes.

[0037] The specific process for detecting forming defects in step S5 includes: capturing the contour image of the current forming layer using a machine vision camera, extracting the contour edge coordinates using an edge detection algorithm, and calculating the deviation between the actual contour size and the design size; if the deviation is greater than a preset deviation threshold, it is determined to be a forming defect, and according to the defect type (collapsed edge, spheroidization, or lack of fusion), the corresponding correction parameters are called from the "Layer Feature-Focus Parameter Mapping Library" to adjust the focal length and spot diameter of the next layer.

[0038] The construction process of the "layer feature-focusing parameter mapping library" in step S2 includes: for different materials to be formed, finite element simulation is used to simulate the molten pool morphology (molten pool depth, width and temperature field distribution) under different layer thicknesses and contour curvatures, and the focusing parameter combination that makes the molten pool morphology meet the forming requirements is selected, a one-to-one correspondence between layer feature data and focusing parameters is established, and stored in the database of the control unit; when the material to be formed is changed, the mapping library can be updated through offline simulation.

[0039] This embodiment provides a collaborative control system for dynamic focusing and layered manufacturing of a selective melting beam, comprising: a dynamic focusing module for acquiring layer feature data of the forming layer and adjusting beam focusing parameters in real time according to collaborative control signals; a collaborative control unit for pre-storing a "layer feature-focusing parameter mapping library", receiving scanning path signals, powder spreading speed signals, and parameter signals from the dynamic focusing module, constructing a three-parameter closed-loop collaborative control logic of "focusing-scanning-powder spreading", and outputting parameter adjustment commands to the dynamic focusing module, scanning drive module, and powder spreading drive module; and a sensing feedback unit for acquiring molten pool state data and forming contour data, transmitting detection signals to the collaborative control unit for the collaborative control unit to determine whether the control parameters of subsequent layers need to be corrected.

[0040] It includes a multi-beam coordination subunit and a defect correction subunit; the multi-beam coordination subunit receives multi-beam molten pool heat-affected zone data collected by the sensing feedback unit and outputs edge beam parameter correction instructions to the coordination control unit; the defect correction subunit receives forming contour defect signals collected by the sensing feedback unit, matches the corresponding correction parameters of the defect from the "layer feature-focusing parameter mapping library", and transmits them to the coordination control unit to adjust the control logic of the next layer.

[0041] Example 2

[0042] This embodiment provides a method for the coordinated control of dynamic focusing of a selective melting beam and layered manufacturing, the specific steps of which are as follows:

[0043] Step S1: Collect the layer feature data of the current forming layer:

[0044] Layer feature data is the fundamental input for dynamic focusing and collaborative control. It is necessary to ensure the real-time nature and accuracy of the acquired data, and to cover the three core dimensions of actual layer thickness, contour curvature, and feature size. The specific sub-steps are as follows:

[0045] S1.1 Determine the acquisition range and accuracy requirements for layer feature data:

[0046] Based on the design drawings of the part to be molded, clearly define the boundary of the molding area of ​​the current molding layer and delineate the effective range for data acquisition (which must cover the entire contour edge and key internal feature areas of the molding layer); simultaneously, considering the precision requirements of the part, set the acquisition precision threshold for layer feature data; the acquisition precision of the actual layer thickness must be within ±0.005mm, and the acquisition precision of the contour curvature must be within ±0.1mm. -1 Within this range, the acquisition accuracy of feature dimensions (such as the wall thickness of thin-walled parts and the cavity depth of deep-cavity parts) must be within ±0.01mm to ensure that subsequent focusing parameter adjustments can adapt to subtle changes in layer features.

[0047] S1.2 Select a suitable layer feature data acquisition device:

[0048] A laser displacement sensor is used as the core data acquisition device, which must have a sampling frequency of ≥1000Hz to meet real-time requirements. It is also equipped with an image acquisition module to assist in acquiring the contour image of the forming layer for subsequent contour curvature calculation. The acquisition device must establish a data communication connection with the control system of the selective melting equipment to ensure that the acquired data can be transmitted to the control unit in real time, with a communication delay of ≤0.5ms, to avoid data lag affecting control response.

[0049] S1.3 Perform actual layer thickness acquisition operation:

[0050] The laser displacement sensor is controlled to move along the preset scanning path of the forming layer (path spacing ≤ 0.5 mm to ensure coverage of the entire forming layer), and a layer thickness data point is collected at each preset distance (e.g., 0.2 mm). The collected data points are filtered to remove outliers (e.g., abrupt changes in data caused by powder splashing), and the average actual layer thickness h of the current forming layer is calculated. At the same time, the maximum deviation value of the layer thickness is recorded for subsequent determination of whether additional adjustment of the focusing parameters is needed.

[0051] S1.4 Perform contour curvature acquisition operation:

[0052] The image acquisition module captures a complete contour image of the current forming layer, and an edge detection algorithm (such as the Canny algorithm) is used to extract the coordinate data of the contour edges. Based on the contour edge coordinates, the contour is divided into multiple continuous line segment units. For each line segment unit, the least squares method is used to fit an arc, and the radius of curvature R of each arc is calculated. If there are straight line segments in the contour, the radius of curvature of the straight line segments is defined as infinite, ultimately forming curvature distribution data covering the entire contour of the forming layer, thus clarifying the different contour regions.

[0053] S1.5 performs feature size acquisition operation:

[0054] For key features of the forming layer (such as the wall thickness of thin-walled structures, the cavity depth of deep-cavity structures, and the cross-sectional dimensions of variable-section structures), dimensional data are collected at different locations of the features (such as the two ends and the middle of thin-walled structures, the bottom of deep cavities, and the middle of sidewalls) using the fixed-point acquisition mode of laser displacement sensors. The average value of multiple dimensional data for the same feature is taken to obtain the actual dimensions of the current key features of the forming layer, which serves as one of the bases for judging whether the feature forming is qualified.

[0055] Step S2: Call the pre-built "hierarchical feature-focusing parameter mapping library":

[0056] The "hierarchical feature-focusing parameter mapping library" is the core basis for achieving fast matching of focusing parameters. It is necessary to ensure the compatibility of the data in the library with the current layer features, and to handle special cases. The specific sub-steps are as follows:

[0057] S2.1 Determine the triggering conditions for calling the mapping library:

[0058] Once step S1 completes the acquisition of the layer feature data of the current forming layer and the control unit verifies the data integrity (i.e., the actual layer thickness, contour curvature, and feature size data have all been acquired and are not missing), the command to call the mapping library is automatically triggered. If there is missing data, the control unit needs to feed back to the acquisition module and re-execute the acquisition operation of the corresponding missing data until the data is complete.

[0059] S2.2 Verify the compatibility between the current layer feature data and the mapping library data format:

[0060] The control unit reads the underlying data format of the mapping library (including the parameter type, unit, and data range of the layer feature data) and compares it with the format of the layer feature data collected in step S1. For example, it verifies whether the unit of the actual layer thickness is mm, whether the unit of the contour curvature radius is mm, and whether the parameter definition of the feature size is consistent with the mapping library. If there is a format mismatch (such as inconsistent units), the control unit automatically performs data format conversion to ensure that the converted data can accurately match the search dimensions in the mapping library.

[0061] S2.3 performs the retrieval and parameter matching of the mapping library:

[0062] The control unit uses the "actual layer thickness h - contour curvature radius R - feature size" collected in step S1 as the three-dimensional search keywords and performs fuzzy matching in the mapping library (considering that there may be slight fluctuations in the actual layer features, a search deviation within ±5% is allowed); if a unique parameter combination is matched, the optimal focusing parameters corresponding to the combination are extracted, including the reference focal length f0, the reference spot diameter D0, and the reference depth of focus; if multiple similar parameter combinations are matched, the similarity between each combination and the current layer feature data is calculated, and the parameter combination with the highest similarity is selected as the initial focusing parameters.

[0063] S2.4 Mapping library adaptation for handling special layer feature data:

[0064] If the current layer feature data exceeds the existing data range of the mapping library (such as extremely thin-walled layers or contours with ultra-large curvature), the control unit automatically starts the offline melt pool simulation submodule, inputs the current layer feature data and the physical properties of the material to be formed (such as thermal conductivity, melting point, and specific heat capacity), simulates the melt pool morphology (melt pool depth, width, and temperature field distribution) under different focusing parameters, filters out the focusing parameter combination that makes the melt pool morphology meet the forming requirements (such as matching the melt pool depth with the layer thickness, and no over-melting / incomplete fusion phenomena), temporarily adds the combination to the mapping library, and uses it as the focusing parameter of the current layer. At the same time, the feature data of this special layer and the corresponding parameters are recorded to provide data support for the subsequent update and optimization of the mapping library.

[0065] Step S3: Adjust the beam focusing parameters in real time based on layer feature data and mapping library:

[0066] The adjustment of focusing parameters needs to be combined with the dynamic changes of layer features. The focal length, spot diameter, and depth of focus need to be matched in a coordinated manner through precise calculation. The specific sub-steps are as follows:

[0067] S3.1 Extract the initial focusing parameters from the mapping library:

[0068] From the focusing parameter combination matched in step S2, extract the reference focal length f0 (the initial focal length value for the current material to be formed), the reference spot diameter D0 (the initial spot diameter adapted to the reference scanning speed), and the reference depth of focus, and use them as the basis values ​​for adjusting the current layer focusing parameters; at the same time, extract the key coefficients corresponding to the current material, including the layer thickness influence coefficient k1 (determined by the material's thermal conductivity, unit: mm / mm) and the contour curvature influence coefficient k2 (determined by the contour forming accuracy requirements, unit: mm·mm), to prepare for subsequent focal length calculations.

[0069] S3.2 Calculate the target focal length of the current layer:

[0070] Based on the actual layer thickness h and contour curvature radius R collected in step S1, and combined with the reference focal length f0, layer thickness influence coefficient k1, and contour curvature influence coefficient k2 extracted in step S3.1, the target focal length of the current layer is calculated using the following formula:

[0071] f = f0 + k1 × h - k2 × (1 / R);

[0072] Where f is the target focal length of the current forming layer (unit: mm), f0 is the reference focal length (initial focal length value for a specific material, unit: mm), k1 is the layer thickness influence coefficient (determined by the thermal conductivity of the material; the higher the thermal conductivity of the material, the larger the value of k1, unit: mm / mm), h is the actual layer thickness collected in step S1 (unit: mm), k2 is the contour curvature influence coefficient (the higher the contour forming accuracy requirement, the larger the value of k2, unit: mm·mm), and R is the contour curvature radius collected in step S1 (unit: mm). After the calculation is completed, the control unit verifies whether the target focal length f is within the focal length adjustment range of the equipment. If it exceeds the range, the coefficient values ​​of k1 and k2 are adjusted (fine-tuned within ±10%), and the calculation is repeated until the target focal length meets the equipment requirements.

[0073] S3.3 Adjust the dynamic focusing actuator to match the target focal length:

[0074] The control unit converts the target focal length f into a control signal for a dynamic focusing actuator (such as a piezoelectric ceramic-driven focusing lens group), driving the focusing lens group to move along the optical axis and adjusting the lens spacing to achieve precise focal length control. During the adjustment process, the laser displacement sensor monitors the actual position of the focusing lens group in real time and compares it with the target position to form a position closed-loop control, ensuring that the focal length adjustment error is ≤0.01mm. At the same time, the response time of the focal length adjustment is recorded to ensure that the time from the issuance of the control signal to the completion of the focal length adjustment is ≤1ms, meeting the real-time requirements.

[0075] S3.4 Synchronously adjust the spot diameter and depth of focus:

[0076] Based on the target focal length f calculated in step S3.2, and combined with the magnification of the optical system, the spot diameter is adjusted synchronously—when the target focal length increases, the spot diameter increases accordingly (to ensure that the coverage of the molten pool matches the layer thickness), and when the target focal length decreases, the spot diameter decreases accordingly (to ensure the accuracy of contour forming); at the same time, the depth of focus is adjusted so that it covers the thickness range of the current layer (the depth of focus must be ≥ 1.2 times the actual layer thickness) to avoid the focus deviating from the molten pool area due to layer thickness fluctuations; after the adjustment is completed, the uniformity of the spot diameter and the coverage range of the depth of focus are verified by the beam quality detection module to ensure that the forming requirements of the current layer are met.

[0077] IV. Step S4: Construct a three-parameter closed-loop collaborative control logic for "focusing-scanning-powder spreading":

[0078] Three-parameter coordinated control is key to ensuring consistent molding quality. It requires real-time linkage of scanning, powder spreading, and focusing parameters, while also addressing the special needs of multi-beam scenarios. The specific sub-steps are as follows:

[0079] S4.1 Establish a synchronous acquisition mechanism for three parameters:

[0080] The scanning drive module, powder spreading drive module, dynamic focusing module, and control unit are connected via industrial Ethernet. A unified sampling clock (sampling frequency ≥ 1000Hz) is set to achieve synchronous acquisition of scanning path signals, powder spreading speed signals, and focusing parameter signals. The scanning path signal includes the coordinates of the current scanning point, the scanning speed v, and the rate of change of the curvature of the scanning path; the powder spreading speed signal includes the real-time speed v of the powder spreading roller. p The focus parameter signal includes the current actual focal length f. current The current spot diameter D; the collected signal is transmitted in real time to the collaborative control submodule of the control unit to ensure that the data delay is ≤0.3ms.

[0081] S4.2 Set the collaborative control threshold for the three parameters:

[0082] Based on the characteristics of the material to be molded (such as melting point and flowability) and the molding quality requirements, set the coordinated control thresholds for each parameter: including the scanning path curvature change rate threshold (e.g., 10° / mm, when this threshold is exceeded, the scanning speed and spot diameter need to be adjusted), the powder spreading speed fluctuation threshold (e.g., 5%, when this threshold is exceeded, the focal length needs to be adjusted), and the focusing parameter deviation threshold (e.g., ±0.02mm, when the focal length deviation exceeds this threshold, the focusing lens group needs to be readjusted). After the thresholds are set, they are stored in the threshold database of the control unit and can be called and modified according to different materials.

[0083] S4.3 Coordinated adjustment of scanning speed and spot diameter:

[0084] When the rate of change of curvature of the scanning path exceeds a preset threshold (e.g., when the scanning path switches from a straight line segment to a large curvature arc segment), the control unit extracts the current spot diameter D (the actual spot diameter adjusted in step S3.4), and combines it with the reference scanning speed v0 and the reference spot diameter D0 (the initial parameter extracted in step S2) to calculate the target scanning speed v using the following formula:

[0085] v = v0 × (D0 / D);

[0086] Where v is the target scanning speed of the current forming layer (unit: mm / s), v0 is the reference scanning speed (the initial scanning speed value for a specific material, unit: mm / s), D0 is the reference spot diameter (the initial spot diameter matching v0, unit: μm), and D is the current spot diameter after adjustment in step S3 (unit: μm). After calculating the target scanning speed v, the control unit sends a speed adjustment command to the scanning drive module to synchronously reduce the scanning speed (e.g., from 1000 mm / s to 800 mm / s) to ensure that the beam energy input per unit area remains consistent when the curvature of the scanning path changes, thus avoiding edge collapse or over-melting at the contour edge.

[0087] Focus adjustment when S4.4 powder spreading speed fluctuates:

[0088] When the real-time powder spreading speed v is fed back by the powder spreading driver module p Compared with the baseline powder spreading speed v p0 v p0 When the deviation exceeds a preset threshold (e.g., 5%), the control unit calculates the deviation ratio of the powder spreading speed [(v p -v p0 ) / v p0 Combined with the powder spreading speed influence coefficient k5 (determined by powder flowability; the worse the powder flowability, the larger the k5 value, unitless), and the focal length f before the powder spreading speed fluctuation. prev (Focal length adjusted in step S3.3), the adjusted focal length f is calculated using the formula. adjust The formula is as follows:

[0089] f adjust =f prev +k5×(v p -v p0 ) / v p0 ;

[0090] Among them, f adjust To adjust the focal length (unit: mm) after fluctuations in powder spreading speed, f prev The focal length (in mm) before the powder spreading speed fluctuation, k5 is the powder spreading speed influence coefficient (determined by powder flowability, no unit), v p v represents the real-time powder spreading speed (unit: mm / s) collected in step S4.1. p0 The baseline powder spreading speed (unit: mm / s) is used. After the calculation is completed, the control unit sends a focal length adjustment command to the dynamic focusing module. For example, when the powder spreading speed is increased, the focal length is increased to compensate for the change in the required melt pool depth caused by the increase in the amount of powder spread, so as to ensure that the melt pool depth matches the actual layer thickness.

[0091] Coordinated beam adjustment in S4.5 multi-beam shaping scenarios:

[0092] If the current selected area melting adopts multi-beam forming (such as scanning with two or more beams simultaneously), step S4.1 also needs to collect the heat-affected zone data of the molten pool of adjacent beams using an infrared thermal imager, and calculate the overlap area S (unit: mm²) of the heat-affected zone of the molten pool of adjacent beams; the control unit extracts the heat-affected zone compensation coefficient k3 corresponding to the material melting point (the higher the material melting point, the larger the k3 value, unit: mm / mm²), and calculates the focal length correction amount Δf of the edge beams by combining it with the focal length of the center beam, using the following formula:

[0093] Δf = k3 × S;

[0094] Where Δf is the focal length correction of the edge beam relative to the center beam (unit: mm), k3 is the heat-affected zone compensation coefficient (determined by the material melting point, unit: mm / mm²), and S is the overlapping area of ​​the heat-affected zone of the adjacent beam molten pool collected in step S4.1 (unit: mm²). The focal length of the edge beam is adjusted according to Δf (if Δf is positive, the focal length of the edge beam is increased), and the power of the edge beam is appropriately reduced (e.g., reduced by 5%) to reduce the heat superposition in the beam intersection area, avoid overheating deformation or splicing seams, and ensure the overall density of multi-beam molding.

[0095] Step S5: Collect molten pool state and forming contour data, and correct subsequent parameters in real time.

[0096] By leveraging feedback from the molten pool state and the forming contour, dynamic correction of control parameters is achieved, forming a closed-loop control. The specific sub-steps are as follows:

[0097] S5.1 Deploy equipment for acquiring molten pool status and forming contour:

[0098] Inside the forming chamber of the selective melting equipment, a high-speed infrared thermometer (sampling rate ≥ 5000 Hz) is installed to collect the temperature of the molten pool, and a machine vision camera (resolution ≥ 2000 × 2000 pixels) is installed to capture the forming outline. The installation position of the acquisition equipment must ensure that it covers the entire forming area and does not affect the beam scanning and powder spreading operation. The temperature measurement range of the high-speed infrared thermometer must cover the melting point of the material to be formed to the melting point + 500℃, and the shooting frequency of the machine vision camera must be synchronized with the layer forming cycle (e.g., take a picture immediately after each layer is formed).

[0099] S5.2 Molten Pool Status Acquisition and Temperature Anomaly Correction:

[0100] A high-speed infrared thermometer collects real-time temperature data T (unit: °C) of the molten pool in the current forming layer. The control unit compares T with the preset optimal molten pool temperature T0 (unit: °C, set according to material properties, usually the material's melting point +100 °C to +200 °C). If T > T0 (i.e., the molten pool temperature is too high, easily leading to overmelting), the control unit extracts the temperature compensation coefficient k4 corresponding to the material's specific heat capacity (the larger the material's specific heat capacity, the larger the k4 value, unit: mm / °C), and combines it with the actual focal length f of the current layer. current (Unit: mm), calculate the target focal length f of the next layer using the formula. comp The formula is as follows:

[0101] f comp =f current -k4×(T-T0);

[0102] Among them, f comp f is the corrected target focal length for the next layer (in mm). currentHere, k is the actual focal length of the current layer (in mm), k4 is the temperature compensation coefficient (determined by the material's specific heat capacity, in mm / ℃), T is the actual temperature of the current molten pool collected in step S5.2 (in ℃), and T0 is the preset optimal temperature of the molten pool (in ℃); f is calculated. comp Then, it is stored in the focus parameter preset module of the next layer as the reference value for the focus adjustment of the next layer. At the same time, the temperature anomaly and correction parameters are recorded for subsequent parameter optimization.

[0103] S5.3 Molding contour acquisition and defect detection and correction:

[0104] After each layer is formed, the machine vision camera captures a complete outline image of the formed layer. The control unit uses an edge detection algorithm to extract the outline edge coordinates and calculates the deviation between the actual outline dimensions (such as outline diameter and wall thickness) and the design dimensions. If the deviation is less than or equal to a preset deviation threshold (such as ±0.05mm), the current layer is considered to be formed successfully, and no parameter adjustment is required. If the deviation is greater than the preset deviation threshold, a forming defect is identified (such as edge collapse, spheroidization, or lack of fusion).

[0105] If the defect is determined to be a collapsed edge (the contour edge is concave inward), the control unit calls the correction parameters corresponding to the collapsed edge defect from the "layer feature-focus parameter mapping library", increases the focal length and spot diameter of the next layer, improves the coverage of the molten pool, and avoids the collapsed edge again.

[0106] If it is determined to be a spheroidization defect (spherical protrusions formed by melt pool shrinkage), the correction parameters corresponding to the spheroidization defect are called to reduce the focal length and spot diameter of the next layer, reduce the local energy input, and suppress spheroidization.

[0107] If the defect is determined to be an unfusion defect (unfusion gaps exist between layers or regions), the correction parameters corresponding to the unfusion defect are called to increase the focal depth and spot diameter of the next layer, increase the molten pool depth, and ensure sufficient fusion.

[0108] S5.4 Parameter update mechanism for forming closed-loop control:

[0109] The next layer target focal length f calculated in step S5.2 comp The defect correction parameters determined in step S5.3 are integrated into the control parameter package for the next layer and transmitted to the mapping library calling module in step S2 and the focusing parameter adjustment module in step S3. When the next layer starts molding, the control unit directly calls the updated control parameter package to start the "feature acquisition-parameter matching-focus adjustment-cooperative control" process of the next layer, realizing the full closed-loop control of "acquisition-adjustment-detection-correction", ensuring that the molding quality of each layer can be optimized in real time and avoiding defect accumulation.

[0110] This embodiment achieves precise matching of focal length, spot diameter, and the geometric features of the forming layer through dynamic focusing adjustment driven by layer features. This effectively solves forming problems caused by fixed parameters in traditional technologies, such as incomplete fusion in thin-walled parts and over-melting in deep-cavity parts. The closed-loop collaborative control of the three parameters of "focusing-scanning-powder spreading" ensures the stability of energy input per unit area and reduces the problem of inconsistent fusion within the layer caused by fluctuations in a single parameter. The heat-affected zone compensation mechanism in multi-beam scenarios avoids overheating deformation and splicing seams in the beam intersection area, improving the overall forming integrity of large-size parts. The real-time feedback correction of the molten pool state and contour defects forms a closed-loop quality control system for the entire process, significantly reducing the incidence of defects such as edge collapse and spheroidization, while ensuring the stability of the mechanical properties of the parts. The overall solution does not require manual intervention in parameter adjustment, which not only improves forming accuracy and manufacturing efficiency, but also enhances adaptability to different materials and complex structural parts, providing reliable technical support for high-precision and high-stability production in selective melting additive manufacturing.

[0111] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for coordinated control of dynamic focusing of a selective melting beam and layered manufacturing, characterized in that, Includes the following steps: S1. Collect the layer feature data of the current forming layer during the selected area melting and layering manufacturing process. The layer feature data includes at least the actual layer thickness, contour curvature, and feature dimensions. S2. Call the pre-built "layered feature-focusing parameter mapping library". The mapping library establishes the correlation between different layer feature data and the optimal focusing parameters through offline melt pool simulation. The optimal focusing parameters include at least focal length, spot diameter and depth of focus. S3. Based on the layer feature data collected in step S1 and the mapping library called in step S2, the beam focusing parameters are adjusted in real time through the dynamic focusing actuator to achieve the adaptation of the current forming layer focusing parameters and layer features. S4. Synchronously acquire scanning path signal, powder spreading speed signal and beam focusing parameter signal to construct a three-parameter closed-loop collaborative control logic of "focusing-scanning-powder spreading". When any parameter exceeds the preset threshold, the other two types of parameters are adjusted synchronously. S5. Collect the melt pool status data and forming contour data of the current forming layer. If an abnormal melt pool or forming defect is detected, correct the focusing parameters and collaborative control threshold of the next layer in real time to form a closed-loop control.

2. The method according to claim 1, characterized in that, When adjusting the beam focusing parameters in real time as described in step S3, the target focal length needs to be determined comprehensively by combining the reference focal length, the actual layer thickness, and the contour curvature: based on the reference focal length corresponding to a specific material, the focal length is adjusted according to the change in the actual layer thickness by using the layer thickness influence coefficient determined by the material's thermal conductivity; at the same time, the focal length is further adjusted according to the change in the contour curvature radius by using the curvature influence coefficient determined by the contour forming accuracy requirements, so that the focal length adapts to the geometric characteristics of the current layer.

3. The method according to claim 1, characterized in that, In the "focus-scan-powder spreading" three-parameter closed-loop collaborative control logic described in step S4, the scanning speed and the spot diameter need to be adjusted in tandem: with the reference scanning speed and reference spot diameter corresponding to a specific material as a reference, when the spot diameter is adjusted according to the layer characteristics, the scanning speed needs to be adjusted synchronously to ensure that the beam energy input per unit area remains consistent, and to avoid over-melting or non-fusion due to changes in spot size.

4. The method according to claim 1, characterized in that, When the selected area melting adopts multi-beam forming, step S4 also includes coordinated adjustment between beams: for edge beams, the focal length of the edge beam relative to the center beam needs to be adjusted according to the overlapping area of ​​the heat-affected zone of the adjacent beam molten pool and the heat-affected zone compensation coefficient determined by the melting point of the material, so as to reduce the thermal superposition deformation in the beam intersection area and avoid the formation of splicing seams.

5. The method according to claim 1, characterized in that, The process of real-time correction of the focal length of the next layer if an abnormal molten pool temperature is detected in step S5 is as follows: when the actual temperature of the molten pool exceeds the preset optimal temperature range, the focal length of the next layer is reduced according to the temperature difference and the temperature compensation coefficient determined by the specific heat capacity of the material. By reducing the spot size, the local energy input is reduced, so that the molten pool temperature returns to the optimal range.

6. The method according to claim 1, characterized in that, In step S4, when the powder spreading speed fluctuates, the focal length needs to be adjusted accordingly: using the reference powder spreading speed as a reference, calculate the deviation ratio between the real-time powder spreading speed and the reference powder spreading speed, and combine the powder spreading speed influence coefficient determined by the powder flowability to adjust the current focal length to ensure that the melt pool depth still meets the molding requirements when the powder spreading amount changes.

7. The method according to claim 1, characterized in that, The specific process for detecting forming defects in step S5 includes: capturing the contour image of the current forming layer using a machine vision camera, extracting the contour edge coordinates using an edge detection algorithm, and calculating the deviation between the actual contour size and the design size; if the deviation is greater than a preset deviation threshold, it is determined to be a forming defect, and according to the defect type, including: edge collapse, spheroidization, or lack of fusion; calling the corresponding correction parameters from the "Layer Feature-Focus Parameter Mapping Library" to adjust the focal length and spot diameter of the next layer.

8. The method according to claim 1, characterized in that, The construction process of the "layer feature-focusing parameter mapping library" in step S2 includes: for different materials to be formed, finite element simulation is used to simulate the molten pool morphology under different layer thicknesses and contour curvatures, and the focusing parameter combination that makes the molten pool morphology meet the forming requirements is selected, a one-to-one correspondence between layer feature data and focusing parameters is established, and the data is stored in the database of the control unit; when the material to be formed is changed, the mapping library can be updated through offline simulation.

9. A collaborative control system for dynamic focusing of a selective melting beam and layered manufacturing, characterized in that, include: Dynamic focusing module: used to acquire layer feature data of the forming layer and adjust the beam focusing parameters in real time according to the collaborative control signal; Collaborative control unit: pre-stores "layer feature-focusing parameter mapping library", receives scanning path signal, powder spreading speed signal and parameter signal of dynamic focusing module, constructs "focusing-scanning-powder spreading" three-parameter closed-loop collaborative control logic, and outputs parameter adjustment commands to dynamic focusing module, scanning drive module and powder spreading drive module; Sensing feedback unit: used to acquire molten pool state data and forming contour data, transmit detection signals to collaborative control unit, and let collaborative control unit determine whether the control parameters of subsequent layers need to be corrected.

10. The system according to claim 9, characterized in that, It also includes a multi-beam coordination subunit and a defect correction subunit; the multi-beam coordination subunit receives multi-beam molten pool heat-affected zone data collected by the sensing feedback unit and outputs edge beam parameter correction instructions to the coordination control unit; the defect correction subunit receives forming contour defect signals collected by the sensing feedback unit, matches the corresponding correction parameters of the defect from the "layer feature-focusing parameter mapping library", and transmits them to the coordination control unit to adjust the control logic of the next layer.

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