Support-free forming method in multi-laser additive and subtractive composite manufacturing

Abstract

The invention relates to an unsupported forming method in multi-laser additive and subtractive composite manufacturing, and belongs to the technical field of additive manufacturing. According to the method, a three-laser cooperative working system is adopted and comprises a continuous optical fiber laser used for SLM additive manufacturing, a femtosecond laser used for macroscopic subtractive machining and a picosecond laser used for microcosmic subtractive finish machining. Through an intelligent partition scanning strategy, a thermal stress layer-by-layer regulation and control technology and a real-time monitoring feedback system, high-precision support-free manufacturing of metal parts is achieved. According to the method, firstly, fused deposition of a main body structure is completed through continuous laser, then macroscopic contour finishing and removing are conducted through femtosecond laser, and finally surface micromachining and fine feature forming are conducted through picosecond laser. The forming quality of a suspension structure and a low-angle inclined plane is remarkably improved, the problems of material waste, complex post-treatment and the like caused by a traditional supporting structure are solved, and high-efficiency and high-performance integrated manufacturing of a complex metal structural part is achieved.

Description

Technical Field

[0001] This invention belongs to the field of metal additive manufacturing technology, specifically relating to a supportless forming method in multi-laser additive and subtractive composite manufacturing. Background Technology

[0002] Laser selective melting (LSM), a key technology in metal additive manufacturing, typically requires the addition of support structures when dealing with geometries such as overhanging structures, large-angle features, and complex internal flow channels. These support structures not only increase material consumption and printing time but also necessitate subsequent mechanical removal or chemical treatment, which may lead to surface damage, residual stress, or even structural deformation of the parts.

[0003] Current unsupported forming technology faces several key technical challenges: warping and deformation in overhanging areas, poor surface quality due to powder adhesion, and dimensional accuracy issues caused by thermal stress accumulation. While existing research attempts to improve these issues by optimizing scanning strategies, adjusting laser parameters, or using multi-laser technologies, it remains difficult to simultaneously guarantee forming efficiency, surface accuracy, and mechanical properties. Traditional single-laser SLM technology, when processing overhanging structures, suffers from insufficient support from the lower layer to the upper layer, leading to unstable molten pools and defects such as spheroidization and warping. Although dual-laser systems can improve these problems to some extent, they still cannot completely eliminate thermal stress accumulation and surface quality issues. While the concept of additive-subtractive composite manufacturing has been proposed, it is mostly limited to macroscopic subtractive manufacturing or applications of single micromachining lasers, failing to fully leverage the synergistic advantages of different lasers. Summary of the Invention

[0004] In order to solve the technical problems existing in the prior art, the purpose of this invention is to provide a supportless forming method in multi-laser additive and subtractive composite manufacturing to solve the above-mentioned technical problems.

[0005] The method provided by this invention is a supportless forming method that integrates continuous laser additive manufacturing, ultrafast laser subtractive manufacturing and online monitoring, and is applicable to the manufacturing of high-precision complex parts in aerospace, medical device and other fields.

[0006] The purpose of this invention is to completely eliminate the support structures required in traditional additive manufacturing processes and provide a supportless forming method for multi-laser additive-subtractive composite manufacturing. The core idea of ​​this invention is to innovatively integrate three laser systems with different characteristics (continuous-wave laser, femtosecond laser, and picosecond laser) onto a single additive manufacturing platform. Through energy gradient zoning and the synergistic effect of two different ultrafast laser sublimation processes between layers, the continuous-wave laser is responsible for the melting and deposition of the main structure, the femtosecond laser for macroscopic sublimation and preliminary finishing, and the picosecond laser for microscopic sublimation and final surface treatment. The three lasers work together to achieve high-performance supportless forming of complex structures, reducing material waste by more than 30%. Zonal energy control combined with online feedback reduces residual stress to <50MPa and dimensional accuracy to ±0.05mm, meeting aerospace cleanroom standards.

[0007] According to a first aspect of the present invention, the present invention provides a supportless forming method in multi-laser additive and subtractive composite manufacturing, comprising the following steps: (1) Additive manufacturing steps (main body forming using a continuous fiber laser): After preheating the substrate, selective laser melting (SLM) additive manufacturing is performed on the preheated substrate using a continuous fiber laser according to the workpiece model. Through intelligent partition scanning strategy and thermal stress control technology, the unsupported forming of the overhanging structure is achieved, and a one-layer forming part is obtained. (2) Macro subtraction step: The macro subtraction process of the one-layer molded part described in step (1) is performed by a femtosecond laser to remove excess material and perform preliminary contour trimming to obtain the molded part after macro subtraction. (3) Micro subtractive process: Picosecond laser is used to perform interlayer micro subtractive finishing on the shaped part after macro subtractive processing in step (2) (to achieve high-precision surface treatment and fine feature forming). (4) Repeat steps (1)-(3) above until the workpiece model is printed and the unsupported workpiece is obtained.

[0008] In some implementations, the intelligent partitioning scanning strategy in step (1) includes: based on the geometric features and support status of each layer of the workpiece, the algorithm adaptively identifies the angle θ between all surfaces and the horizontal plane, marks the area where θ < 45° and the area directly below is loose powder or suspended, and divides it into a hanging area; then it is determined whether the area directly below each position of the layer is a formed solid metal structure. If it has sufficient rigid support and θ ≥ 45°, it is divided into a solid area; finally, the empty area between the boundary of the solid area and the hanging area is divided into a transition area of ​​"buffer zone" (in some implementations, if there is no empty area between individual solid areas and hanging areas, then no transition area is set between the solid area and the hanging area, and the solid area and the hanging area are connected). Its range is dynamically adjusted according to the position and shape of each hanging area, without a fixed angle threshold, and is only used to alleviate the sudden change of thermal gradient. Different laser power, scanning speed and scanning spacing parameters are used for laser selective melting additive manufacturing in different areas of each layer. The intelligent partitioned scanning strategy dynamically divides each layer into solid, transition, and overhang regions based on different parts of the layer, and uses different combinations of laser power, scanning speed, and scanning spacing parameters for each region. By precisely controlling the heat input in different regions, it actively manages and counteracts the inherent thermal stress and deformation during the SLM process, thereby achieving high-quality forming without the need for physical support.

[0009] In some embodiments, the laser power of the selective laser melting additive manufacturing in the solid region is 250-300W, the scanning speed is 900-1100mm / s, and the scanning spacing is 0.1-1.2mm; the laser power of the selective laser melting additive manufacturing in the transition region is 150-200W, the scanning speed is 1200-1400mm / s, and the scanning spacing is 0.07-0.1mm; and the laser power of the selective laser melting additive manufacturing in the overhanging region is 80-120W, the scanning speed is 1400-1600mm / s, and the scanning spacing is 0.05-0.07mm.

[0010] In some embodiments, the laser power of the selective laser melting additive manufacturing in the solid region is 250-300W, the scanning speed is 1000mm / s, and the scanning spacing is 0.1mm; the laser power of the selective laser melting additive manufacturing in the transition region is 150-200W, the scanning speed is 1200mm / s, and the scanning spacing is 0.08mm; and the laser power of the selective laser melting additive manufacturing in the overhanging region is 80-120W, the scanning speed is 1500mm / s, and the scanning spacing is 0.06mm.

[0011] The overhanging area is printed using a low-power (80-120W), scanning speed of 1500mm / s, and scanning spacing of 0.06mm parameter combination. High power generates significant localized thermal stress, which the weak foundation cannot withstand, inevitably leading to warping and deformation. Using low power produces a shallow and small molten pool, just enough to melt the powder in the current layer and create a slight and controllable metallurgical bond with the underlying layer, thus maximizing the protection of the loose powder below and ensuring the successful construction of the overhanging structure. The solid portion, on the other hand, is printed using high power (250-300W), a scanning speed of 1000mm / s, and a scanning spacing of 0.1mm; this produces a sufficiently large and deep molten pool to completely melt the metal powder and achieve a strong metallurgical bond with the underlying solid layer. Simultaneously, sufficient heat input removes any micropores that may have existed in the previous process, ensuring the mechanical properties and forming quality of the part. The area between the low-power overhanging area and the high-power solid area is a transition zone. The large thermal gradient between low and high power is the main cause of cracks and deformation. Therefore, the transition zone is printed with a combination of parameters: medium power (150-200W), scanning speed of 1200mm / s, and scanning spacing of 0.08mm. As a "buffer zone", the heat input changes smoothly from low to high, which mitigates the thermal gradient and avoids interface cracks or deformation that may be caused by sudden stress changes.

[0012] In some implementations, the thickness of each layer during the SLM molding process is 25-35 μm.

[0013] In some implementations, in step (1), the tilt angle θ of the overhang structure is less than 45°; in the selective laser melting additive manufacturing (SLM) process, a gradient margin of 70-90 μm is reserved for the interlayer macro subtractive processing in step (2), and a gradient margin of 15-25 μm is reserved for the interlayer micro subtractive finishing in step (3).

[0014] In some embodiments, the temperature of the substrate preheating in step (1) is 180-200°C.

[0015] In the method provided by this invention, step (1) applies different laser parameters to different areas through a partitioned scanning strategy. The core printing area is controlled to have a high-energy laser input, with reciprocating scanning to ensure interlayer metallurgical bonding. The overhanging area is controlled to have a low-energy laser input, where powder particles absorb energy and convert it into heat. Since the thermal conductivity of loose powder is only 0.1–1% of that of solid metal, the local temperature rapidly rises above the melting point to form a molten pool. Simultaneously, the low heat input reduces the size of the molten pool and gravity-induced sagging, suppressing warping.

[0016] After printing the current layer in the overhanging area, the adjacent solid area is printed, connecting the overhanging structure to form a complete cross-section of the part to be processed. On critical surfaces and in the overhanging area, after each SLM layer is completed, femtosecond laser is used for rough subtractive machining, followed by picosecond laser for precision subtractive machining. This process continues layer by layer until the part is completely printed and removed.

[0017] In an optional implementation, a digital model of the target component is first acquired. The 3D CAD model is then subjected to overhang structure identification and automatic partitioning, dividing the model into a core area and an overhang area. Corresponding scanning paths and laser parameters are generated for different areas. Deformation prediction and geometric compensation are performed on the overhang area to offset potential deformation during printing. The 3D model is imported, the slice layer thickness is set, and a subtractive material gradient allowance is reserved.

[0018] In an optional implementation, a layer of metal powder is first laid on the substrate before printing begins. Then the substrate is preheated. After reaching the preheating temperature, a continuous laser irradiates a specific area according to the layer information of the CAD model to melt the powder and begin printing.

[0019] In an alternative implementation, unlike conventional layers, the first layer requires a higher energy input to ensure that the molten metal can fully penetrate the powder layer and achieve a strong metallurgical bond with the substrate. In some implementations, the angle between the cutting direction and the normal of the layer in the interlayer macro subtractive processing step (2) is controlled within ±5°.

[0020] In some embodiments, the pulse energy of the femtosecond laser in step (2) is 300-600 μJ, and the femtosecond laser pulse removes the spheroids, sputterings, and unfused particles generated in the selective laser melting additive manufacturing process (SLM forming process) in step (1). The femtosecond laser pulse is used for macroscopic contour trimming and preliminary surface finish treatment.

[0021] In an optional implementation, a femtosecond laser is used to remove spheroids, sputterings, and unfused particles from the edges of the overhanging area for macroscopic contour trimming and preliminary surface finishing. Otherwise, it will affect the powder spreading quality and laser focusing of subsequent layers, leading to defect accumulation.

[0022] In some embodiments, the single-layer cutting depth during the interlayer micro-subtractive finishing process in step (3) is 2-5 μm, and the angle between the cutting direction and the layer normal is controlled within ±2°; the repetition frequency of the picosecond laser pulse is ≥ 500 kHz. Micron-level surface processing is performed using picosecond laser pulses to shape fine features, process surface textures, and refine high-precision contours.

[0023] In some implementations, the pulse energy of the picosecond laser in step (3) is 35-65 μJ.

[0024] In an alternative implementation, picosecond lasers are used to remove surface powder and microscopic defects, processing fine features and high-precision contours.

[0025] In some implementations, during the workpiece printing process, the processing parameters and scanning paths of the continuous laser, femtosecond laser, and picosecond laser are dynamically adjusted through a real-time monitoring and feedback system to ensure the quality of workpiece forming; In some implementations, the laser selective melting additive manufacturing in step (1), the interlayer macro subtractive processing in step (2), and the interlayer micro subtractive finishing in step (3) are carried out in a cycle on the same additive manufacturing platform and in the same coordinate system until the part is manufactured.

[0026] The real-time monitoring and feedback system integrates various high-precision monitoring devices such as infrared thermal imagers and high-speed cameras to collect key data during the processing in real time, continuously track changes in the molten pool temperature, and capture behaviors such as molten pool spatter. Based on this data, the system dynamically adjusts the processing parameters and scanning paths of the three lasers, thereby achieving inter-layer collaborative optimization and ensuring stable and efficient workpiece forming quality. In some implementations, the real-time monitoring feedback system uses the monitoring data from the infrared thermal imager, high-speed camera, and spot analyzer. The built-in intelligent algorithm of the device instantly compares and diagnoses these real-time data with the preset process quality model. Once a deviation is identified, the decision module immediately generates specific adjustment instructions based on the preset rule base and immediately sends them to the corresponding laser and galvanometer actuators. This enables online and automatic correction of laser parameters and scanning paths, controlling the temperature fluctuation of the molten pool in the overhanging area within ±20°C to ensure the workpiece forming quality.

[0027] In an optional implementation, after the part (workpiece) is printed, the powder in the molding chamber is cleaned, and then the printed sample and substrate are taken out and the final part is obtained after wire cutting.

[0028] In alternative implementations, high energy input is typically achieved by reducing the scanning speed or increasing the laser power.

[0029] This invention achieves high-precision supportless manufacturing of metal parts through intelligent partitioned scanning strategy, layer-by-layer thermal stress control technology, and real-time monitoring and feedback system. The method first completes the molten deposition of the main structure using continuous laser, then uses femtosecond laser for macroscopic contour trimming and removal, and finally employs picosecond laser for surface micro-machining and fine feature shaping.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The “low-power” parameter strategy adopted by this invention for the overhanging area fundamentally reduces heat input and lowers the temperature gradient between the molten pool and the surrounding materials. It fundamentally avoids surface damage, deformation or stress concentration of the parts that may be caused by the removal of the support, thus ensuring the inherent performance and quality of the parts.

[0031] (2) The intermittent subtractive process using femtosecond and picosecond lasers employed in this application naturally constitutes a cooling interval for additive manufacturing, providing time for stress relaxation of the material. The subtractive process itself removes some of the material under high stress, thus also playing a role in stress release.

[0032] (3) In this application, the "additive-subtractive" process is carried out cyclically on the same equipment and in the same coordinate system, which realizes the unification of the processing benchmark and avoids the errors caused by multiple clamping and positioning. The femtosecond laser removes sputtering, spheroidization and unfused particles from each layer in time, providing a clean and flat printing substrate for the next layer, suppressing the accumulation of defects in the process and ensuring the accuracy of the macroscopic contour. The picosecond laser performs micron-level milling and polishing on the surface, which can improve the final surface roughness to the precision level, and can even be used directly as a functional surface, eliminating the need for subsequent machining or polishing processes.

[0033] (4) The multi-laser additive and subtractive unsupported forming method used in this application is highly efficient and easy to operate. It completely eliminates the need for designing and using physical supports, saving a large amount of expensive metal powder and directly reducing manufacturing costs. It eliminates cumbersome post-processing steps such as support removal, grinding, and polishing, significantly shortening the total time from printing to obtaining usable parts, improving overall manufacturing efficiency, and fundamentally avoiding surface damage, deformation, or stress concentration of parts that may be caused by support removal. This ensures the inherent properties and quality of the parts, greatly improving the forming success rate and geometric stability of complex structural parts, and has significant economic value and promotional significance. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the SLM forming process provided in Embodiment 1 of this application.

[0036] Figure 2 This is a schematic diagram of an SLM-formed overhang structure provided in Embodiment 1 of this application.

[0037] Figure 3This is a schematic diagram of femtosecond laser subtractive material provided in Embodiment 1 of this application.

[0038] Figure 4 This is a schematic diagram of picosecond laser subtractive material provided in Embodiment 1 of this application.

[0039] Figure 5 This is a schematic diagram of unsupported multi-laser additive and subtractive forming provided in Embodiment 1 of this application.

[0040] Figure 6 This application provides a schematic diagram of a complex structure including a large-angle air film pore in Embodiment 1.

[0041] Figure 7 This is the three-dimensional morphology of the unsupported surface formed by multi-laser additive and subtractive materials in Embodiment 5 of this application.

[0042] Figure 8 This is the three-dimensional morphology of the unsupported surface formed by multi-laser additive and subtractive materials in Comparative Example 11 of this application. Detailed Implementation

[0043] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the described embodiments are merely 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.

[0044] Example 1 A supportless forming method for multi-laser additive and subtractive composite manufacturing includes the following steps: (1) Laser selective melting additive manufacturing is carried out using a continuous fiber laser based on the model of the workpiece. Through intelligent partition scanning strategy and thermal stress control technology, the unsupported forming of the suspended structure is realized, and a one-layer forming part is obtained. (2) A femtosecond laser is used to perform interlayer macro subtraction on the one-layer molded part described in step (1). The single-layer cutting depth during the interlayer macro subtraction process is 30-50 μm, and the molded part after macro subtraction is obtained. (3) Use a picosecond laser to perform interlayer micro subtractive finishing on the macro subtractive material processed in step (2) to obtain the micro subtractive material processed part; (4) Repeat steps (1)-(3) above until the workpiece model is printed and the unsupported workpiece is obtained.

[0045] As an example, refer to Figure 6 As shown, Figure 6 This application provides a schematic diagram of a complex structure including a large-angle air film pore (θ ≈ 25°) in Embodiment 1.

[0046] Specifically, before printing begins, the workpiece model (3D CAD model) undergoes the following preprocessing.

[0047] Overhang structure identification: Analyze the angles (θ) between all surfaces of the model and the horizontal plane.

[0048] Surfaces with θ < 45° are defined as "critical overhang surfaces," which are the core areas requiring unsupported treatment. Surfaces with θ < 30° are defined as "extreme overhang surfaces," requiring the most stringent parameters and strategies. The top surfaces of long-span bridging structures (such as horizontal connections between two supports) and enclosed cavities are also considered suitable for unsupported treatment.

[0049] 3D volume partitioning: The algorithm does not only identify surfaces, but also voxels the entire 3D model entity and dynamically divides it into three types of regions based on its spatial location and geometric features. Figure 2 This is a schematic diagram of the SLM-formed overhang structure provided in Embodiment 1 of this application: Solid Region: The area within this layer's cross-section that is adequately supported by the underlying solid material, or the solid core of the part. Strategy Goal: To ensure high density and mechanical properties, and to pursue molding efficiency. Overhanging Region: The area within this layer's cross-section where powder or air is directly below, lacking solid support (θ < 45°). Strategy Goal: To suppress heat input, control melt pool behavior, prevent collapse and spheroidization, and prioritize molding stability over extreme density. Transition Region: The region between the core region and the overhanging region. Strategy Goal: To smoothly transition parameters and strategies between the core and overhanging regions, avoiding abrupt performance changes and alleviating stress concentration.

[0050] Specifically, all overhanging surfaces with θ < 45° were identified, with the lower surface of the air film pores being the extreme overhanging surface (θ ≈ 25°). The leaf 3D model was voxelized and divided into: solid regions such as the leaf root and crown; overhanging regions including the lower surface of the air film pores and the leading edge of the leaf blade; and transition regions in the middle of the leaf blade. Slices and parameters were set with a layer thickness of 30 μm; allowances for material reduction were reserved: 80 μm per layer for macroscopic material reduction and 20 μm per layer for microscopic material reduction.

[0051] The intelligent partition scanning strategy in step (1) includes: Based on the geometric features and support status of each layer of the workpiece, the algorithm adaptively identifies the angle θ between all surfaces and the horizontal plane layer by layer, marking areas where θ < 45° and there is loose powder or suspension directly below, and classifying these areas as overhanging areas; then it is determined whether there is a formed solid metal structure directly below each position of the layer. If there is sufficient rigid support and θ ≥ 45°, it is classified as a solid area; finally, a transition area is generated between the boundary of the solid area and the overhanging area, and then laser selective melting additive manufacturing is performed on different areas of each layer using different laser power, scanning speed and scanning spacing parameters.

[0052] This embodiment involves a layer-by-layer implementation without support forming. The complete printing cycle of a typical layer (including a layer with a hanging structure) is described in detail below: First, the substrate is preheated to 200°C, and a uniform layer of 316 stainless steel powder is laid on the formed previous layer using a squeegee. The powder laying process requires a smooth process to ensure that the powder bed above the overhanging area is also flat and dense. This powder will act as a "soft support" for the molten pool, and the powder laying thickness is consistent with the layer thickness (30μm).

[0053] Secondly, SLM continuous laser zonal scanning Figure 1 This is a schematic diagram of the SLM forming process provided in Embodiment 1 of this application. A laser galvanometer guides a continuous laser beam to scan according to the pre-processed partition path and parameters. The scanning order is crucial: Specifically, the thermal stress treatment in step (1) involves the following steps: First, the laser precisely scans the boundary contour between the overhanging area and the solid / transition area at a high power (270W) and a low scanning speed (850mm / s). The purpose of this is to form a complete and robust molten border, creating a solid "dam" or "anchor" for the overhanging area, confining the unmelted powder within the area and preventing the molten metal from flowing. Subsequently, the laser switches to the solid area laser parameters and performs a high-speed, high-energy-density scan to fill the area (solid area power set at 300W, scanning speed at 1000mm / s, and scanning spacing at 0.1mm). A checkerboard or striped scanning strategy is typically used (Example 1 uses a checkerboard scanning strategy), dividing the large area into 10mm² islands with a 100-500ms delay between islands to disperse thermal stress. After the solid area is completed, the transition area is immediately scanned with transition area parameters (transition area power set at 220W, scanning speed at 1200mm / s, and scanning spacing at 0.08mm). The parameter changes are gradual to ensure good fusion with the core area. The overhanging area is scanned last (power set at 120W, scan speed at 1500mm / s, scan spacing at 0.06mm). This allows the solid area and transition area above it as much time as possible to cool, providing them with stronger rigid support.

[0054] This embodiment employs a "low power + short vector" strategy: Specifically, low power and short vector (90W, 0.5mm): significantly reduce linear energy density, avoiding melting through the underlying powder "soft support". Small scanning spacing (0.05mm) ensures sufficient overlap between scan lines, avoiding incomplete fusion. The extremely short scanning vector (0.5mm) divides the overhang area into tiny regions at the millimeter or even sub-millimeter level, using a random scanning sequence: after rapidly scanning each small region, the laser jumps to another distant region (the distance between the currently scanned region and another distant region is 4mm), leaving sufficient delay time (50-200ms) to allow the heat of the currently scanned region to dissipate fully, preventing heat accumulation. Edge-inward scanning: when scanning the overhang area, the laser scanning path starts from the edge of the solidified overhang area contour and fills inward, using the rigidity of the edge to stabilize the internal molten pool.

[0055] In step (1) of this embodiment, a 1kW continuous fiber laser with a spot diameter of 80μm is used.

[0056] The physical area is set with a power of 300W, a scanning speed of 1000mm / s, and a scanning spacing of 0.1mm. The transition zone is set with a power of 220W, a scanning speed of 1200mm / s, and a scanning spacing of 0.08mm. The power of the overhang area is set to 120W, the scanning speed to 1500mm / s, and the scanning interval to 0.06mm. Step (2) of femtosecond laser interlayer subtraction (macroscopic processing) is described in detail below (refer to...). Figure 3 As shown, Figure 3 (This is a schematic diagram of femtosecond laser subtractive processing provided in Embodiment 1 of this application) Specifically, after each layer of SLM forming is completed by the continuous fiber laser in step (1) (i.e., a layer of formed part is obtained), a femtosecond laser is activated to perform SLM forming macro-subtraction (interlayer macro-subtraction processing) on ​​the layer of formed part. The laser parameters in this step are set as follows: pulse energy 500μJ, repetition frequency 100kHz, and scanning speed 500mm / s. The galvanometer system guides the femtosecond laser focus to be precisely positioned on the edge and lower surface of the overhanging structure. The angle between the cutting direction and the normal of the layer in the femtosecond laser interlayer subtraction (macro-processing) process is controlled within ±5°. The single-layer cutting depth is 40μm.

[0057] Step (2) utilizes the "cold processing" characteristic of femtosecond lasers to precisely remove spheroidized particles and sintered powder adhering to the edges through ablation. This is crucial for ensuring the quality of the next layer of powder coating; if not removed, these particles will cause unevenness in subsequent layers. The femtosecond laser pulse removes the spheroidized particles, sputtered material, and unfused particles generated during the selective laser melting additive manufacturing process in step (1).

[0058] The overhanging profile, which has slightly shrunk and deformed due to the surface tension of the molten pool, is trimmed at the micron level to restore it to its theoretical geometric dimensions, providing a precise reference platform for subsequent layers.

[0059] Step (3) of picosecond laser interlayer subtraction (microscopic processing) is described in detail below (refer to...). Figure 4 As shown, Figure 4 This is a schematic diagram of picosecond laser subtractive processing provided in Embodiment 1 of this application.

[0060] Specifically, after completing each layer of additive manufacturing (laser selective melting additive manufacturing in step (1)) and femtosecond subtractive manufacturing (interlayer macro subtractive processing in step (2)), a picosecond laser is activated; the laser parameters are set as follows: pulse energy 50 μJ, repetition frequency 1 MHz, and scanning speed 1000 mm / s. The angle between the cutting direction and the layer normal is controlled within ±2° during the interlayer micro subtractive finishing process (picosecond laser interlayer subtractive process). The single-layer cutting depth is 4 μm during the interlayer micro subtractive finishing process.

[0061] Picosecond lasers are used to remove microscopic protrusions and deposits from surfaces with precision. Through slight ablation by high-frequency pulses, the surface is smoothed, reducing roughness from over 10 μm to below 3 μm.

[0062] Real-time monitoring and dynamic adjustment Throughout the entire workpiece printing process, the real-time monitoring and feedback system operates continuously, as described below.

[0063] The real-time monitoring and feedback system compares the monitoring data from the infrared thermal imager, high-speed camera, and spot analyzer with the preset process quality model in an instant, thereby dynamically adjusting the processing parameters and scanning paths of the continuous laser, femtosecond laser, and picosecond laser.

[0064] Specifically, if the infrared thermal imager detects an abnormal temperature rise at a point in the overhanging area, the system will immediately instruct subsequent scanning paths to bypass that point, or automatically reduce the laser power in that area by 10%-20%. If the high-speed camera detects violent splashing or abnormal enlargement of the molten pool, the system will determine that the parameters at that point are mismatched, and automatically shorten the scanning vector or increase the point spacing, and apply the corrected parameters in subsequent similar overhanging areas.

[0065] The real-time monitoring and feedback system uses data from infrared thermal imagers, high-speed cameras, and spot analyzers. The built-in intelligent algorithm of the equipment instantly compares and diagnoses these real-time data with the preset process quality model. Once a deviation is identified, the decision module immediately generates specific adjustment instructions based on the preset rule base and sends them to the corresponding laser and galvanometer actuators. This enables online and automatic correction of laser parameters and scanning paths, controlling the temperature fluctuation of the molten pool in the overhanging area within ±20°C.

[0066] Repeating After completing steps (1)-(3) above, the forming platform descends by one layer thickness, the powder spreading system re-spreads the powder, and the next printing cycle begins. Steps (1)-(3) are repeated until the printing is completed according to the workpiece model, resulting in an unsupported formed workpiece (e.g., Figure 5 (As shown).

[0067] Example 2 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared to Example 1, the power of the suspension area is adjusted to 100W.

[0068] Example 3 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared to Example 1, the power in the transition zone is adjusted to 180W.

[0069] Example 4 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared with Example 1, the femtosecond laser single-layer cutting depth was adjusted to 40 μm.

[0070] Example 5 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared with Example 1, the picosecond laser single-layer cutting depth was adjusted to 3 μm. Figure 7 The surface morphology of the unsupported surface formed by multi-laser additive and subtractive materials in Embodiment 5 of this application is 1.1 μm.

[0071] Example 6 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared to Example 1, the macroscopic material reduction allowance was adjusted to 70 μm.

[0072] Example 7 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared with Example 1, the micro-subtractive margin was adjusted to 25 μm.

[0073] Example 8 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared to Example 1, the scanning speed of the solid region was adjusted to 900 mm / s.

[0074] Example 9 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared with Example 1, the preheating temperature of the substrate was adjusted to 180°C.

[0075] Example 10 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared to Example 1, the picosecond laser repetition frequency was adjusted to 800 kHz.

[0076] Comparative Example 1 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared to Example 1, the power of the suspension area described in this comparative example is 180W.

[0077] Comparative Example 2 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared with Example 1, this comparative example does not use a partitioned scanning strategy, and the entire area uniformly adopts the entity area parameters.

[0078] Comparative Example 3 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared with Example 1, this comparative example does not involve femtosecond laser macroscopic subtractive processing.

[0079] Comparative Example 4 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared to Example 1, this comparative example did not undergo picosecond laser micro-subtractive processing.

[0080] Comparative Example 5 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared to Example 1, the layer thickness in this comparative example is set to 50 μm.

[0081] Comparative Example 6 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared to Example 1, the macroscopic material reduction allowance in this comparative example is set to 50 μm.

[0082] Comparative Example 7 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared to Example 1, the substrate described in this comparative example is not preheated.

[0083] Comparative Example 8 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared to Example 1, the femtosecond laser pulse energy in this comparative example is set to 200 μJ.

[0084] Comparative Example 9 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared to Example 1, the picosecond laser pulse energy of this comparative example is set to 10 μJ.

[0085] Comparative Example 10 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared to Example 1, this comparative example does not have a real-time monitoring and feedback system.

[0086] Comparative Example 11 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared with Example 1, the single-layer cutting depth of the femtosecond laser macro subtractive material described in this comparative example is set to 60 μm. Figure 8 The three-dimensional morphology of the unsupported surface formed by multi-laser additive and subtractive materials in Comparative Example 11 of this application is shown, with a surface roughness of 12.5 μm.

[0087] Comparative Example 12 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared with Example 1, the single-layer cutting depth of the femtosecond laser macro subtractive material described in this comparative example is set to 20 μm.

[0088] Comparative Example 13 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared with Example 1, the single-layer cutting depth of the picosecond laser microsublimation described in this comparative example is set to 8 μm.

[0089] Comparative Example 14 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared with Example 1, the single-layer cutting depth of the picosecond laser micro-sublimation described in this comparative example is set to 1 μm.

[0090] Comparative Example 15 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared with Example 1, the comparative example describes a 50 μm macroscopic gradient margin reserved for femtosecond laser subtraction during the SLM additive manufacturing process.

[0091] Comparative Example 16 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared with Example 1, the comparative example describes a 100μm macroscopic gradient margin reserved for femtosecond laser subtraction in the SLM additive manufacturing process.

[0092] Comparative Example 17 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared with Example 1, in the SLM additive manufacturing process described in this comparative example, a micro-gradient margin of 10 μm is reserved for picosecond laser subtraction.

[0093] Comparative Example 18 A supportless forming method for multi-laser additive and subtractive composite manufacturing, wherein the steps unless otherwise specified are the same as in Example 1, the difference being: Compared with Example 1, in the SLM additive manufacturing process described in this comparative example, a micro-gradient margin of 30 μm is reserved for picosecond laser subtraction.

[0094] The above samples were subjected to performance testing, and the experimental testing methods are as follows: Test method for molding quality: Determined according to national standard GB / T 36591-2018; Surface roughness test method: Refer to national standard GB / T 1031-2009; Test method for dimensional accuracy: Determined in accordance with the national standard GB / T 39331-2020.

[0095] The test results of Examples 1-10 and Comparative Examples 1-18 are shown in the table below: Table 1. Test results of Examples 1-10 and Comparative Examples 1-18 As can be seen from Table 1, the forming quality, roughness, and dimensional accuracy of each embodiment of the present invention have outstanding comprehensive performance compared with each comparative example, which demonstrates the reliability, repeatability, and superiority of the multi-laser additive and subtractive unsupported process scheme of the present invention.

[0096] The method provided in this invention employs a three-laser collaborative system, including a continuous fiber laser for SLM additive manufacturing, a femtosecond laser for macroscopic subtractive processing, and a picosecond laser for microscopic subtractive finishing. Through intelligent partitioned scanning strategies, layer-by-layer thermal stress control technology, and a real-time monitoring and feedback system, high-precision supportless manufacturing of metal parts is achieved. This method first completes the molten deposition of the main structure using a continuous laser, then uses a femtosecond laser for macroscopic contour trimming and removal, and finally employs a picosecond laser for surface micromachining and fine feature shaping. This significantly improves the forming quality of overhanging structures and low-angle inclined surfaces, eliminates the material waste and complex post-processing problems associated with traditional support structures, and achieves high-efficiency, high-performance integrated manufacturing of complex metal structural parts.

[0097] In summary, the supportless forming method in multi-laser additive and subtractive composite manufacturing provided in this application can effectively improve the surface quality of the formed sample and realize high-efficiency, high-performance integrated manufacturing of complex metal structural parts.

[0098] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for supportless forming in multi-laser additive-subtractive hybrid manufacturing, characterized in that, It comprises the following steps: (1) After preheating the substrate, laser selective melting additive manufacturing is carried out on the workpiece model by using a continuous fiber laser, through intelligent partition scanning strategy and thermal stress control technology, the overhanging structure is formed without support, and a layer of formed part is obtained; (2) The layer of formed part in step (1) is subjected to interlayer macro-subtractive machining by using a femtosecond laser, and a macro-subtractive machined formed part is obtained; (3) The macro-subtractive machined formed part in step (2) is subjected to interlayer micro-subtractive finishing machining by using a picosecond laser, and a micro-subtractive machined formed part is obtained; (4) Repeat steps (1)-(3) until the workpiece model is printed to obtain a workpiece formed without support.

2. The method of claim 1, wherein, The intelligent partition scanning strategy in step (1) comprises: Based on the geometric characteristics and support state of each layer of the workpiece, the algorithm is used to automatically identify the angle θ between all surfaces and horizontal planes layer by layer, mark the area where θ<45° and the loose powder or overhanging area below, and divide it into overhanging area; Then judge whether the position below each layer is an already formed solid metal structure, if it has sufficient rigid support and θ≥45°, it is divided into solid area; Finally, in the empty area between the boundary of the solid area and the overhanging area, it is divided into transition area, then different laser power, scanning speed and scanning pitch parameters are used for laser selective melting additive manufacturing in different areas of each layer.

3. The method of claim 2, wherein, The laser power of laser selective melting additive manufacturing in the solid area is 250-300 W, the scanning speed is 900-1100 mm / s, and the scanning pitch is 0.1-1.2 mm; The laser power of laser selective melting additive manufacturing in the transition area is 150-200 W, the scanning speed is 1200-1400 mm / s, and the scanning pitch is 0.07-0.1 mm; The laser power of laser selective melting additive manufacturing in the overhanging area is 80-120 W, the scanning speed is 1400-1600 mm / s, and the scanning pitch is 0.05-0.07 mm.

4. The method of claim 2, wherein, The thickness of each layer is 25-35 μm.

5. The method of claim 1, wherein, In step (1), the inclination angle θ of the overhanging structure is < 45°; During the laser selective melting additive manufacturing process in step (1), 70-90 μm of gradient allowance is reserved for the interlayer macro-subtractive machining in step (2), and 15-25 μm of gradient allowance is reserved for the interlayer micro-subtractive finishing machining in step (3); The preheating temperature of the substrate in step (1) is 180-200℃.

6. The method of claim 1, wherein, The single layer cutting depth of the interlayer macro-subtractive machining process in step (2) is 30-50 μm, and the angle between the cutting direction and the normal direction of the layer is controlled within ±5°.

7. The method of claim 1, wherein, The pulse energy of the femtosecond laser in step (2) is 300-600 μJ, which removes the spheroidization, sputtering and unmelted particles generated in the laser selective melting additive manufacturing process in step (1) by femtosecond laser pulses.

8. The method of claim 1, wherein, The single-layer cutting depth in the interlayer micro-subtractive finishing process of step (3) is 2-5 μm, the included angle between the cutting direction and the normal of the layer is controlled within ± 2°, the repetition frequency of the picosecond laser pulse is ≥ 500 kHz, and the pulse energy of the picosecond laser in step (3) is 35-65 μJ.

9. The method according to any one of claims 1 to 8, wherein, In the workpiece printing process, the processing parameters and scanning paths of the continuous laser, femtosecond laser and picosecond laser are dynamically adjusted through real-time monitoring feedback system to ensure the forming quality of the workpiece; the laser selective melting additive manufacturing in step (1), the interlayer macro-subtractive machining in step (2) and the interlayer micro-subtractive finishing in step (3) are cyclically carried out in the same additive manufacturing platform and the same coordinate system.

10. The method of claim 9, wherein, The real-time monitoring feedback system compares the monitoring data of the infrared thermal imager, high-speed camera and light spot analyzer with the preset process quality model in real time to dynamically adjust the processing parameters and scanning paths of the continuous laser, femtosecond laser and picosecond laser, and control the molten pool temperature fluctuation of the overhanging area within ± 20°C.

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