Laser energy field auxiliary suspension structure unsupported additive manufacturing system and method

Abstract

The invention discloses a laser energy field auxiliary suspension structure unsupported additive manufacturing system and method. The system comprises a forming machining unit, an energy field auxiliary unit and an online monitoring unit. The energy field auxiliary unit comprises a second laser device and a laser collimator, the second laser device is an energy field auxiliary preheating laser device, the paraxial position of the energy field auxiliary preheating laser device is arranged outside the powder bed fusion forming cabin, and an emergent light beam of the energy field auxiliary preheating laser device is used for locally preheating the powder bed in the printing process after being processed by the laser collimator; the online monitoring unit comprises an industrial camera, an optical tomography camera and a control and analysis unit; the industrial camera and the optical tomography camera are respectively used for collecting a sedimentary layer image and a molten pool light intensity signal in a printing process; and the control and analysis unit receives online monitoring data from the industrial camera and the optical tomography camera, and analyzes and processes images and signals. The paraxial energy field assists in preheating the laser, and controllability and forming quality of support-free forming are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of laser powder bed melting technology, specifically relating to a laser energy field-assisted unsupported additive manufacturing system and method for suspended structures. Background Technology

[0002] The heavy reliance on support structures in laser powder bed melting technology limits its widespread application in the manufacture of complex components. Support structures not only increase material consumption, post-processing costs, and manufacturing cycles, but more importantly, they restrict the geometric freedom of design. For components with internal cavities, flow channels, or integrated lattice-skin structures, traditional supports are often impossible to install or difficult to remove. Therefore, developing supportless forming technology is a key challenge in driving this technology towards high-performance, high-complexity manufacturing. Under supportless conditions, the forming quality of overhanging areas is a major challenge. Taking lattice-skin structures as an example, horizontal or near-horizontal overhanging areas on the lower surface of the skin are prone to macroscopic cracks and severe warping under conventional process parameters. The fundamental reason lies in the extremely high temperature gradient, rapid cooling, and complex thermal cycling accompanying the laser powder bed melting process, leading to the accumulation of significant residual stress within the part. In the overhanging areas, because the thermal conductivity of the unmelted powder below is much lower than that of a dense solid, heat is more easily accumulated, forming localized high-temperature zones, thus exacerbating thermal stress concentration. If the process parameters are not properly matched, the accumulated tensile stress will induce warping deformation or even cracking in the overhanging area; at the same time, the molten pool is prone to flow instability due to the lack of solid support, resulting in surface collapse or spheroidization, which seriously affects the forming accuracy and component performance.

[0003] To address these challenges, online monitoring and active thermal management have become key technological approaches. Industrial cameras, as a non-contact monitoring method, can perform real-time imaging and visual analysis of the surface state after powder bed melting and molten metal deposition; optical tomography systems can acquire real-time light intensity signals from the molten pool to analyze its dynamic behavior. Online monitoring methods based on these two technologies have been gradually applied to forming quality tracking, molten pool behavior analysis, and defect early warning. Laser powder bed melting is essentially a dynamic thermal process, and its forming quality is highly dependent on the thermal equilibrium state of the system. Traditional methods typically manage the overall temperature field by controlling interlayer cooling time or using substrate preheating to reduce temperature gradients and alleviate residual stress. However, interlayer cooling time is constrained by part geometry and is difficult to control flexibly; substrate preheating has a limited range of influence, and its effect on deep structures or local features gradually diminishes, failing to meet the precise requirements of local thermal management for complex structures. Summary of the Invention

[0004] The purpose of this invention is to provide a laser energy field-assisted unsupported additive manufacturing system and method for suspended structures, solving the problems of fracture and warping deformation in unsupported printed suspended structures.

[0005] The technical solution adopted in this invention is:

[0006] A laser energy field-assisted suspended structure unsupported additive manufacturing system includes a forming processing unit, an energy field auxiliary unit, and an online monitoring unit. The forming processing unit includes a powder bed melting chamber, a first laser, a galvanometer system, a doctor blade powder spreading system, a protective gas system, and a substrate. The energy field auxiliary unit includes a second laser and a laser collimator. The second laser is an energy field-assisted preheating laser, which is off-axis positioned outside the powder bed melting chamber. Its emitted beam is processed by the laser collimator and used to locally preheat the powder bed during the printing process.

[0007] The online monitoring unit includes an industrial camera, an optical tomography camera, and a control and analysis unit. The industrial camera and the optical tomography camera are both off-axis mounted outside the powder bed fusion molding chamber, and are used to acquire images of the deposited layer and light intensity signals of the molten pool during the printing process, respectively. The control and analysis unit consists of a computer, which is located outside the powder bed fusion molding chamber. The computer receives online monitoring data from the industrial camera and the optical tomography camera, and analyzes and processes the images and signals.

[0008] Furthermore, the first laser is a 1064nm Yb fiber laser, and the second laser is an 808nm semiconductor laser.

[0009] A laser energy field-assisted unsupported additive manufacturing method for a suspended structure includes the following steps:

[0010] S1: The surface images of the deposited layer after the powder is spread by the scraper and after the powder is melted by the first laser are acquired layer by layer by an industrial camera, and the images are corrected by perspective transformation to monitor the formation appearance and obtain appearance images.

[0011] S2: The optical intensity time-series signal of the molten pool is acquired layer by layer by an optical tomography camera, and the signal is stitched together based on the time-domain integration method to obtain the dynamic information of the molten pool.

[0012] S3: After forming is completed, use an optical scanner to collect point cloud data of the formed part, reconstruct the three-dimensional solid model of the formed part, register and compare the three-dimensional solid model with the original design three-dimensional model, analyze the geometric deviation between the two, and then quantitatively evaluate the forming accuracy of the part.

[0013] S4: By combining the original three-dimensional design model of the formed part, the reconstructed three-dimensional solid model, and the appearance state images and dynamic information of the molten pool during the forming process, the spatiotemporal evolution law of fracture and warping deformation defects that occur in the part during forming is obtained.

[0014] S5: Based on the analysis of the spatiotemporal evolution of defects, a laser energy field-assisted unsupported additive manufacturing strategy for suspended structures is proposed.

[0015] S6: Perform three-dimensional geometric analysis and slicing layering on the original three-dimensional model of the part to be formed, identify its overhanging area and the corresponding number of layers, and then determine the preheating area, start and end layers and corresponding preheating temperature requirements that require laser energy field assisted preheating by the second laser.

[0016] S7: Based on the preheating area, start and stop layers and corresponding preheating temperature requirements, the spot size, output power, action position and action sequence of the second laser are designed and configured in a coordinated manner.

[0017] S8: During the formation of the suspended structure, unsupported additive manufacturing is implemented. Powder melting and forming of the first laser and energy field-assisted preheating of the second laser are performed simultaneously in the suspended area. The second laser provides continuous and controllable auxiliary heat input to the suspended area.

[0018] Further, step S1 includes the following steps:

[0019] S11: An industrial camera is mounted off-axis outside the powder bed melting and forming chamber. After each layer of powder is spread by the powder-spreading scraper, the surface image of that layer is acquired synchronously. Then, after the first laser of that layer melts the powder, the surface image is acquired synchronously again.

[0020] S12: Use preset calibration parameters to perform perspective transformation correction on the surface images after powder spreading and after melting to eliminate the angular distortion caused by the tilted installation of the camera, thereby obtaining the appearance state images for real-time monitoring and subsequent analysis.

[0021] Further, step S2 includes the following steps:

[0022] S21: An optical tomography camera is mounted off-axis outside the powder bed melting and forming chamber to collect the time-series signal of the light intensity radiated by the molten pool in real time during the melting process of the first laser in each layer of powder.

[0023] S22: The time-series signal is processed using the time-domain integration method, and the dynamic information of the molten pool reflecting the light intensity distribution of the molten pool is reconstructed using an image stitching algorithm.

[0024] Further, step S3 includes the following steps:

[0025] S31: After forming is completed, use an optical scanner to perform a three-dimensional scan on all surfaces of the formed part and collect point cloud data of the formed part.

[0026] S32: The point cloud data is processed by reverse engineering software to reconstruct a three-dimensional solid model of the formed part;

[0027] S33: Using analysis software, the three-dimensional solid model of the formed part is spatially registered and compared with the original design three-dimensional model. The geometric deviation distribution between the two is analyzed, and the critical dimension deviation of the overhang area is calculated, thereby quantitatively evaluating the final forming accuracy of the part.

[0028] Furthermore, S4 specifically includes: comparing and analyzing the original design three-dimensional model of the formed part, the reconstructed three-dimensional solid model, and the appearance state image and molten pool dynamic information during the forming process; identifying and locating the starting layer and spatial position of fracture and warping deformation defects; and then, based on the occurrence sequence and morphological evolution of defects in each layer, visualizing and extracting the spatiotemporal evolution process of the defects to obtain the spatiotemporal evolution law of fracture and warping deformation defects.

[0029] Furthermore, S5 specifically includes: proposing a laser energy field-assisted unsupported additive manufacturing strategy for overhanging structures based on the spatiotemporal evolution law of fracture and warping deformation defects; using a second laser to perform in-situ, directional, and adjustable preheating on the overhanging area to achieve active control of local thermal stress, thereby effectively suppressing the tendency of fracture and warping deformation.

[0030] Further, step S6 includes the following steps:

[0031] S61: Import the original design 3D model into the 3D modeling software, and identify all overhanging areas and their local geometry with an angle less than a preset threshold to the horizontal direction through geometric analysis;

[0032] S62: Slice and layer the original design 3D model to obtain the contour information of each printing layer. Based on the spatial relationship between the overhang area and each layer, determine the printing layer number containing the overhang area and its spatial coordinates within the layer.

[0033] S63: Combining the local geometry of the overhanging region, the spatiotemporal evolution of fracture and warping deformation defects, and the determined spatial coordinates of the overhanging region, determine the spatiotemporal locations where fracture and warping are prone to occur, and then determine the key preheating region and its starting and ending layers that need to be preheated with laser energy field assistance by a second laser.

[0034] S64: Based on the local geometry of the overhanging area and the key dimensional deviations of the overhanging area obtained in step S3 under non-preheating conditions, determine the preheating temperature process requirements for the corresponding preheating area.

[0035] Further, step S7 includes the following steps:

[0036] S71: Based on the overhanging area and its local geometry determined in step S6, match and design the spot size of the second laser, and plan the precise action position of the second laser spot on the powder bed.

[0037] S72: Based on the preheating temperature process requirements of the preheating area determined in step S6, set the output power, action sequence and start / stop control logic of the second laser to form a preheating process parameter set that works in conjunction with the first laser, and complete the overall system configuration of the second laser energy field.

[0038] Compared with the prior art, the technical effects of the present invention include:

[0039] (1) This invention takes large-format horizontal overhanging structures as the research object and systematically explores their typical failure behaviors in the unsupported forming process. It fills the gap in the research of unsupported additive manufacturing process for large-size horizontal overhanging structures in this field. Based on the online monitoring method, this invention reveals the evolution law of edge fracture, warping and deformation of large-format horizontal overhanging structures in unsupported forming, and proposes a laser energy field assisted unsupported additive manufacturing method for overhanging structures.

[0040] (2) In contrast, although adjusting the power and scanning speed of the forming laser can indirectly affect the thermal state of the molten pool, this method has a complex control mechanism and simultaneously affects the forming and preheating effects of the molten pool. The parameter window is narrow, which can easily lead to over-melting or insufficient energy. In contrast, this invention uses an independent off-axis preheating laser, whose energy input is decoupled from the forming laser. It can independently and accurately control the preheating energy without the need for complex iterative optimization of printing parameters, making the operation simpler and more reliable. In contrast, although increasing the interlayer cooling time helps to dissipate heat and reduce residual stress, it will significantly extend the overall printing cycle and seriously restrict production efficiency, especially for large or high-rise zero-layer printing. Manufacturing components is not economical. This invention performs local preheating simultaneously during the printing process, without interrupting or extending the interlayer waiting time. While ensuring thermal management, it maximizes manufacturing efficiency. In contrast, substrate preheating improves the overall temperature field by heating the forming substrate, but its heat-affected zone decreases sharply with increasing printing height, and its effect on the upper and middle overhanging structures is very limited, making it difficult to achieve precise temperature control along the height direction. The off-axis preheating laser of this invention can move the focus synchronously with the printing process to achieve directional heating of overhanging areas at different heights, without being limited by height. The heat input position and energy can be adjusted in real time.

[0041] (3) The off-axis laser preheating of the present invention achieves fixed-point, timed, and quantitative heat energy replenishment and deformation suppression of the overhanging area through a simple setup independent of the forming system without interfering with the normal printing process. This method not only solves the inherent limitations of traditional methods in terms of control complexity, efficiency loss and range of action, but also significantly improves the controllability and forming quality of unsupported forming with flexible heat management that is "heated as needed".

[0042] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the integration of a paraxial-assisted laser energy field system.

[0044] Figure 2 This is a flowchart of the laser energy field-assisted unsupported additive manufacturing method for suspended structures according to the present invention.

[0045] Figure 3 This is a multi-source signal monitoring diagram of the closure process of the suspended structure without laser energy field assistance.

[0046] Figure 4 This is a typical forming failure morphology diagram of a suspended structure without laser energy field assistance.

[0047] Figure 5 The image shows the spot morphology and energy distribution of the laser energy field.

[0048] Figure 6 Comparison of the forming results of the suspended structure under different laser energy field temperatures.

[0049] Figure 7 Multi-source signal monitoring diagram for the closure process of the suspended structure preheated at 300℃ with the aid of an energy field.

[0050] Figure 8 This is a diagram showing the distribution of geometric deviations in high-risk areas of a suspended structure under different laser energy field temperatures.

[0051] Figure 9 This is a statistical chart showing the deviation of high-risk areas of suspended structures under different laser energy field temperatures.

[0052] Figure 10 Topographical image of an unsupported additive manufacturing structure assisted by a laser energy field. Detailed Implementation

[0053] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0054] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments of the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or other combinations.

[0055] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0056] Combination Figure 1 A laser energy field-assisted suspended structure unsupported additive manufacturing system includes a forming processing unit, an energy field auxiliary unit, and an online monitoring unit. The forming processing unit includes a powder bed melting and forming chamber, a first laser, a galvanometer system, a doctor blade powder spreading system, a protective gas system, and a substrate. The energy field auxiliary unit includes a second laser and a laser collimator. The second laser is an energy field-assisted preheating laser, which is off-axis positioned outside the powder bed melting and forming chamber. Its emitted beam is processed by the laser collimator and used to locally preheat the powder bed during the printing process.

[0057] The online monitoring unit includes an industrial camera, an optical tomography camera, and a control and analysis unit. The industrial camera and the optical tomography camera are both off-axis mounted outside the powder bed fusion molding chamber, and are used to acquire images of the deposited layer and light intensity signals of the molten pool during the printing process, respectively. The control and analysis unit consists of a computer, which is located outside the powder bed fusion molding chamber. The computer receives online monitoring data from the industrial camera and the optical tomography camera, and analyzes and processes the images and signals.

[0058] Preferably, the first laser is a 1064nm Yb fiber laser, and the second laser is an 808nm semiconductor laser.

[0059] Combination Figure 2 A laser energy field-assisted unsupported additive manufacturing method for a suspended structure includes the following steps:

[0060] S1: The surface images of the deposited layer after the powder is spread by the scraper and after the powder is melted by the first laser are acquired layer by layer by an industrial camera, and the images are corrected by perspective transformation to monitor the formation appearance and obtain appearance images.

[0061] S2: The optical intensity time-series signal of the molten pool is acquired layer by layer by an optical tomography camera, and the signal is stitched together based on the time-domain integration method to obtain the dynamic information of the molten pool.

[0062] S3: After forming is completed, use an optical scanner to collect point cloud data of the formed part, reconstruct the three-dimensional solid model of the formed part, register and compare the three-dimensional solid model with the original design three-dimensional model, analyze the geometric deviation between the two, and then quantitatively evaluate the forming accuracy of the part.

[0063] S4: By combining the original three-dimensional design model of the formed part, the reconstructed three-dimensional solid model, and the appearance state images and dynamic information of the molten pool during the forming process, the spatiotemporal evolution law of fracture and warping deformation defects that occur in the part during forming is obtained.

[0064] S5: Based on the analysis of the spatiotemporal evolution of defects, a laser energy field-assisted unsupported additive manufacturing strategy for suspended structures is proposed.

[0065] S6: Perform three-dimensional geometric analysis and slicing layering on the original three-dimensional model of the part to be formed, identify its overhanging area and the corresponding number of layers, and then determine the preheating area, start and end layers and corresponding preheating temperature requirements that require laser energy field assisted preheating by the second laser.

[0066] S7: Based on the preheating area, start and stop layers and corresponding preheating temperature requirements, the spot size, output power, action position and action sequence of the second laser are designed and configured in a coordinated manner.

[0067] S8: During the formation of the suspended structure, unsupported additive manufacturing is implemented. Powder melting and forming of the first laser and energy field-assisted preheating of the second laser are performed simultaneously in the suspended area. The second laser provides continuous and controllable auxiliary heat input to the suspended area.

[0068] Furthermore, S1 specifically includes:

[0069] S11: The industrial camera is mounted off-axis to the outside of the powder bed melting chamber via a fixed bracket. The mounting diagram is as follows: Figure 2 As shown, during the part forming process, the surface image of each layer is synchronously acquired after the powder spreading scraper completes the powder spreading at a set frame rate of 2Hz. Subsequently, the surface image is synchronously acquired again after the first laser of the layer completes the powder melting.

[0070] S12: Perspective transformation correction is performed on the surface images after powder spreading and after melting using preset calibration parameters to eliminate angular distortion caused by the tilted camera installation. This yields surface state images for real-time monitoring and subsequent analysis. The processing effect is as follows: Figure 3 As shown.

[0071] Furthermore, S2 specifically includes:

[0072] S21: The optical tomography camera is mounted off-axis to the outside of the powder bed melting chamber via a tripod. A schematic diagram of the mounting is shown below. Figure 1 As shown, during the part forming process, the molten pool light intensity signal when the first 1064nm laser interacts with the powder is synchronously acquired at a set frame rate of 2Hz.

[0073] S22: Multiple frames of signal images from the same deposition layer are superimposed and enhanced using a time-series integration method, and then the images are corrected based on pre-calibrated perspective transformation parameters. The processing effect is as follows: Figure 3 As shown.

[0074] Furthermore, S3 specifically includes:

[0075] S31: After forming is completed, use an optical scanner to perform a three-dimensional scan on all surfaces of the formed part and collect point cloud data of the formed part.

[0076] S32: The point cloud data is processed using FreeScan reverse engineering software to reconstruct a three-dimensional solid model of the formed part, and exported as an STL format file for subsequent analysis.

[0077] S33: Import the 3D solid model STL file and the original design 3D model STL file into the geometric analysis software CloudCompare for registration and comparison to obtain the geometric deviation distribution data of the specimen, such as... Figure 4 As shown, no macroscopic cracking or warping was observed in the 20mm wide sample, while significant overall upward warping was observed in the 40mm and 50mm wide samples.

[0078] Furthermore, S4 specifically includes:

[0079] By comparing and analyzing the original 3D design model of the formed part, the reconstructed 3D solid model, and the appearance images and molten pool dynamic information during the forming process, the starting layer and spatial location of fracture and warping deformation defects are identified and located. Furthermore, based on the temporal sequence and morphological evolution of defects between layers, their spatiotemporal evolution process is visualized and its patterns are extracted, resulting in... Figure 3 The defect evolution pattern is shown as follows: In the first layer, the loose powder beneath the overhanging area caused molten pool instability, leading to a continuous abnormal molten pool light intensity signal. After scanning, local thermal anomalies and cracking appeared. In the second layer, although the overall molten pool light intensity signal improved due to the solid deposition below, significant local anomalies still appeared in the upper right, accompanied by stronger thermal anomalies and warping after scanning. In the third layer, although the molten pool light intensity signal in the overhanging area continued to improve, severe local anomalies and heat accumulation occurred in the lower right, ultimately causing the entire sample to warp, resulting in mechanical interference and interruption of printing.

[0080] Furthermore, S5 specifically includes:

[0081] Based on the quantitative results of forming accuracy in step S3 and the analysis of defect evolution in step S4, it is clear that in the unsupported forming of large-format overhanging structures, uneven temperature gradients lead to residual stress concentration on the surface, which in turn causes fracture and warping deformation in the overlap area, ultimately resulting in forming failure. Introducing a second laser energy field can significantly reduce the temperature gradient and thermal stress in this area, thereby improving the morphology of the overhanging surface and effectively suppressing structural fracture and warping deformation. The heating conditions, steady-state temperature data, and distribution of the second laser energy field acting on the powder bed were calibrated and acquired using thermocouples and infrared thermal imagers, respectively. Figure 5 As shown in the figures, (a) is a schematic diagram of temperature measurement, (b) is the temperature field distribution at 300℃, (c) is the temperature variation curve of the powder at the center and edge of the laser spot over time, and (d) is the temperature variation of the center and edge of the laser spot with the current. Based on this, a laser energy field-assisted unsupported additive manufacturing strategy for suspended structures is proposed to achieve active control of thermal stress, thereby suppressing the tendency of fracture and warping in this region.

[0082] Furthermore, S6 specifically includes:

[0083] S61: Import the original design 3D model of the suspended structure specimen into SolidWorks 3D modeling software, and identify all horizontal suspended areas and their local geometry in the model through geometric analysis;

[0084] S62: Slice and layer the original design 3D model to obtain the contour information of each printing layer. Based on the spatial intersection relationship between the overhang area and each layer, determine the printing layer number containing the overhang area and the forming space coordinates within the corresponding layer.

[0085] S63: Based on the local geometry of the overhanging region, the spatiotemporal evolution of fracture and warping deformation defects, and the determined spatial coordinates of the overhanging region, and according to the overhanging height of 1 mm, the layer thickness of 0.03 mm, and the alloy strength of Ti6Al4V, it is determined that the first 10 layers of the overhanging region need to be preheated by the laser energy field assisted by the first laser.

[0086] S64: Based on the geometric characteristics of the overhang area as a 36mm horizontal plane, and the critical dimension deviation of 2.11mm in the overhang area measured in step S3 under the condition of no preheating, the preheating temperature process requirement for the corresponding critical area is determined to be 300℃.

[0087] Furthermore, S7 specifically includes:

[0088] S71: Based on the geometric features of the 36mm overhang area of ​​the part determined in step S6, a circular light spot with a diameter of 50mm is matched and designed.

[0089] S72: Based on the preset temperature requirements of this area, the output current of the preheating laser is set to 7.5A, corresponding to a temperature of 300℃; based on the starting and ending layers of the horizontally suspended area that needs to be preheated, the timing of the second laser's action and the start / stop control logic are determined, forming a set of preheating process parameters that coordinate with the forming laser scanning, and completing the overall system configuration of the preheating laser energy field.

[0090] Furthermore, S8 specifically includes:

[0091] Based on the spatial coordinates of the overhanging area on the powder bed in step S6, the second laser head is mounted off-axis to the outside of the forming chamber at a fixed angle and pose via a robotic arm. During the part forming process, the overhanging area of ​​the current powder bed is preheated according to the process parameters configured in step S7.

[0092] The apparent state image and molten pool dynamic information obtained in steps S1 and S2 are combined, such as Figure 6 As shown, although fractures still exist in the horizontal overhang area in the first four layers, the defects do not further evolve into warping deformation; by the 14th layer, the fracture area has completely healed, and the entire forming process is successfully completed. The geometric deviation distribution between the 3D solid model of the formed part and the original design 3D model is analyzed using CloudCompare, as shown... Figure 7 As shown, the part was not formed under the condition of preheating assisted by the second laser energy field, but the part was successfully formed under the condition of preheating assisted by the second laser energy field, thus verifying the effectiveness of the laser energy field assisted suspended structure unsupported additive manufacturing method.

[0093] Further experiments were conducted to demonstrate the effectiveness and applicability of using a second laser energy field-assisted preheating method for unsupported additive manufacturing of suspended structures. These experiments included:

[0094] Experiments were conducted on a horizontally suspended component with a span of 36mm, using a second laser for energy field-assisted preheating at 0℃, 100℃, 200℃, and 300℃. The results were compared and analyzed using offline 3D scanning. Figure 7 As shown, parts without laser energy field assistance failed to form, while parts with laser energy field assistance all formed successfully. At different preheating temperatures, the forming quality of the high-risk thermal anomaly area at the end of the scanning path varied: the geometric deviation distribution obtained after registration and comparison using CloudCompare software shows, for example... Figure 8 , Figure 9 As shown, the height deviation at the surface overlap is most severe under preheating at 100℃, followed by 300℃, and the forming accuracy is best under 200℃.

[0095] Unsupported forming experiments were conducted on horizontally suspended surfaces with spans of 16mm, 36mm, and 46mm to achieve 300℃ energy field-assisted preheating of the second laser. For example... Figure 10As shown in the 0℃ preheating data, the 20mm wide sample was successfully formed without the aid of a second laser energy field, while the 40mm and 50mm wide samples both failed to form. Figure 10 As shown in the figure, the 20mm, 40mm and 50mm samples were successfully formed under the preheating condition assisted by the second laser energy field, which confirms the effectiveness and process applicability of the preheating temperature control strategy.

[0096] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A laser energy field-assisted unsupported additive manufacturing system for suspended structures, characterized in that, It includes a forming and processing unit, an energy field auxiliary unit, and an online monitoring unit. The forming and processing unit includes a powder bed melting and forming chamber, a first laser, a galvanometer system, a doctor blade powder spreading system, a protective gas system, and a substrate. The energy field auxiliary unit includes a second laser and a laser collimator. The second laser is an energy field-assisted preheating laser, which is off-axis located outside the powder bed melting and forming chamber. Its emitted beam is processed by the laser collimator and used to perform local preheating of the powder bed during the printing process. The online monitoring unit includes an industrial camera, an optical tomography camera, and a control and analysis unit. The industrial camera and the optical tomography camera are both off-axis mounted outside the powder bed fusion molding chamber, and are used to acquire images of the deposited layer and light intensity signals of the molten pool during the printing process, respectively. The control and analysis unit consists of a computer, which is located outside the powder bed fusion molding chamber. The computer receives online monitoring data from the industrial camera and the optical tomography camera, and analyzes and processes the images and signals.

2. The laser energy field-assisted unsupported additive manufacturing system for suspended structures according to claim 1, characterized in that, The first laser is a 1064nm Yb fiber laser, and the second laser is an 808nm semiconductor laser.

3. A method for unsupported additive manufacturing of a suspended structure assisted by a laser energy field, characterized in that, Includes the following steps: S1: The surface images of the deposited layer after the powder is spread by the scraper and after the powder is melted by the first laser are acquired layer by layer by an industrial camera, and the images are corrected by perspective transformation to monitor the formation appearance and obtain appearance images. S2: The optical intensity time-series signal of the molten pool is acquired layer by layer by an optical tomography camera, and the signal is stitched together based on the time-domain integration method to obtain the dynamic information of the molten pool. S3: After forming is completed, use an optical scanner to collect point cloud data of the formed part, reconstruct the three-dimensional solid model of the formed part, register and compare the three-dimensional solid model with the original design three-dimensional model, analyze the geometric deviation between the two, and then quantitatively evaluate the forming accuracy of the part. S4: By combining the original three-dimensional design model of the formed part, the reconstructed three-dimensional solid model, and the appearance state images and dynamic information of the molten pool during the forming process, the spatiotemporal evolution law of fracture and warping deformation defects that occur in the part during forming is obtained. S5: Based on the analysis of the spatiotemporal evolution of defects, a laser energy field-assisted unsupported additive manufacturing strategy for suspended structures is proposed. S6: Perform three-dimensional geometric analysis and slicing layering on the original three-dimensional model of the part to be formed, identify its overhanging area and the corresponding number of layers, and then determine the preheating area, start and end layers and corresponding preheating temperature requirements that require laser energy field assisted preheating by the second laser. S7: Based on the preheating area, start and stop layers and corresponding preheating temperature requirements, the spot size, output power, action position and action sequence of the second laser are designed and configured in a coordinated manner. S8: During the formation of the suspended structure, unsupported additive manufacturing is implemented. Powder melting and forming of the first laser and energy field-assisted preheating of the second laser are performed simultaneously in the suspended area. The second laser provides continuous and controllable auxiliary heat input to the suspended area.

4. The laser energy field-assisted unsupported additive manufacturing method for a suspended structure according to claim 3, characterized in that, S1 includes the following steps: S11: An industrial camera is mounted off-axis outside the powder bed melting and forming chamber. After each layer of powder is spread by the powder-spreading scraper, the surface image of that layer is acquired synchronously. Then, after the first laser of that layer melts the powder, the surface image is acquired synchronously again. S12: Use preset calibration parameters to perform perspective transformation correction on the surface images after powder spreading and after melting to eliminate the angular distortion caused by the tilted installation of the camera, thereby obtaining the appearance state images for real-time monitoring and subsequent analysis.

5. The laser energy field-assisted unsupported additive manufacturing method for a suspended structure according to claim 4, characterized in that, S2 includes the following steps: S21: An optical tomography camera is mounted off-axis outside the powder bed melting and forming chamber to collect the time-series signal of the light intensity radiated by the molten pool in real time during the melting process of the first laser in each layer of powder. S22: The time-series signal is processed using the time-domain integration method, and the dynamic information of the molten pool reflecting the light intensity distribution of the molten pool is reconstructed using an image stitching algorithm.

6. The laser energy field-assisted unsupported additive manufacturing method for a suspended structure according to claim 5, characterized in that, S3 includes the following steps: S31: After forming is completed, use an optical scanner to perform a three-dimensional scan on all surfaces of the formed part and collect point cloud data of the formed part. S32: The point cloud data is processed by reverse engineering software to reconstruct a three-dimensional solid model of the formed part; S33: Using analysis software, the three-dimensional solid model of the formed part is spatially registered and compared with the original design three-dimensional model. The geometric deviation distribution between the two is analyzed, and the critical dimension deviation of the overhang area is calculated, thereby quantitatively evaluating the final forming accuracy of the part.

7. The laser energy field-assisted unsupported additive manufacturing method for a suspended structure according to claim 6, characterized in that, S4 specifically includes: comparing and analyzing the original design three-dimensional model of the formed part, the reconstructed three-dimensional solid model, and the appearance state image and dynamic information of the molten pool during the forming process; identifying and locating the starting layer and spatial position of fracture and warping deformation defects; and then, based on the occurrence sequence and morphological evolution of defects in each layer, visualizing and extracting the spatiotemporal evolution process of the defects to obtain the spatiotemporal evolution law of fracture and warping deformation defects.

8. The laser energy field-assisted unsupported additive manufacturing method for a suspended structure according to claim 7, characterized in that, Specifically, S5 includes: proposing a laser energy field-assisted unsupported additive manufacturing strategy for overhanging structures based on the spatiotemporal evolution law of fracture and warping deformation defects; using a second laser to perform in-situ, directional, and adjustable preheating of the overhanging area to achieve active control of local thermal stress, thereby effectively suppressing the tendency of fracture and warping deformation.

9. The laser energy field-assisted unsupported additive manufacturing method for a suspended structure according to claim 8, characterized in that, S6 includes the following steps: S61: Import the original design 3D model into the 3D modeling software, and identify all overhanging areas and their local geometry with an angle less than a preset threshold to the horizontal direction through geometric analysis; S62: Slice and layer the original design 3D model to obtain the contour information of each printing layer. Based on the spatial relationship between the overhang area and each layer, determine the printing layer number containing the overhang area and its spatial coordinates within the layer. S63: Combining the local geometry of the overhanging region, the spatiotemporal evolution of fracture and warping deformation defects, and the determined spatial coordinates of the overhanging region, determine the spatiotemporal locations where fracture and warping are prone to occur, and then determine the key preheating region and its starting and ending layers that need to be preheated with laser energy field assistance by a second laser. S64: Based on the local geometry of the overhanging area and the key dimensional deviations of the overhanging area obtained in step S3 under non-preheating conditions, determine the preheating temperature process requirements for the corresponding preheating area.

10. The laser energy field-assisted unsupported additive manufacturing method for a suspended structure according to claim 9, characterized in that, S7 includes the following steps: S71: Based on the overhanging area and its local geometry determined in step S6, match and design the spot size of the second laser, and plan the precise action position of the second laser spot on the powder bed. S72: Based on the preheating temperature process requirements of the preheating area determined in step S6, set the output power, action sequence and start / stop control logic of the second laser to form a preheating process parameter set that works in conjunction with the first laser, and complete the overall system configuration of the second laser energy field.

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