Method for improving the durability of an additive manufacturing dot matrix structure by interlayer thermomechanical action
By leveraging the interlayer thermal effect of picosecond lasers, the stress concentration areas of the lattice structure are identified and strengthened, solving the problem of easy breakage at nodes in laser powder bed melting technology and improving the durability and mechanical properties of the lattice structure.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NANJING UNIV OF AERONAUTICS & ASTRONAUTICS
- Filing Date
- 2026-04-13
- Publication Date
- 2026-07-10
AI Technical Summary
When manufacturing lattice structures, existing laser powder bed melting technology is prone to stress concentration, porosity, and residual tensile stress in the node area, which makes the structure prone to fracture and failure during load-bearing. Traditional impact strengthening technology is difficult to adapt to complex shapes and is prone to introducing thermal effects or impurities.
By utilizing the interlayer thermal effect of picosecond lasers and identifying areas prone to stress concentration through simulation software, local strengthening is achieved by using picosecond laser-induced shock waves to transform residual tensile stress into compressive stress, refine grains, improve microstructure and surface quality, and enhance durability.
It effectively reduces stress concentration at nodes, improves the durability and mechanical properties of lattice structures, avoids thermal deformation and impurity introduction, and achieves precise strengthening effects.
Smart Images
Figure CN122365756A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of additive manufacturing lattice structures, and specifically relates to a method for improving the durability of additive manufacturing lattice structures through interlayer thermal effects. Background Technology
[0002] A lattice structure typically refers to a porous structure with a non-random geometry, generally constructed from multiple repeatable units (unit cells) arranged periodically in space. Lattice structures possess advantages such as ultralight weight, high porosity, high specific strength, and good energy absorption characteristics, combining both structural and functional features, making them widely applicable in the manufacturing of high-end aerospace equipment. Traditional porous materials are usually prepared using methods such as investment casting, wire weaving, foaming, and powder metallurgy, but their lattices often exhibit randomness, and their porosity and wall thickness cannot be precisely controlled. Facing the more stringent requirements of the aerospace field for lattice structures, complex lattice structures are almost impossible to obtain through traditional processing methods, leading to a dilemma where lightweight and complex lattice structures can be designed but not manufactured. The emergence of additive manufacturing technology has solved this problem, especially metal additive manufacturing technology based on laser powder bed melting (LPBF), which has become a crucial technology for obtaining lattice structures due to its unique advantage in manufacturing highly complex structures. However, during the laser additive manufacturing of lattice structures, the nodal regions are prone to a series of defects due to multiple heat accumulations, unstable molten pool flow, and stress concentration caused by rapid solidification: firstly, anisotropic mechanical properties caused by coarse columnar grains; secondly, porosity, microcracks, and residual tensile stress; and thirdly, high surface roughness and insufficient density. Under load, these defects make the nodal regions weak points in the lattice structure, making them highly susceptible to fracture and ultimately leading to lattice structure failure.
[0003] Laser shock peening is an effective means of improving the mechanical properties of materials. By irradiating the material surface to generate plasma shock waves, residual compressive stress is introduced and a stable dislocation structure is formed, which can significantly improve the material's performance. Existing laser shock peening technologies mainly include mechanical shot peening and nanosecond laser shock peening, but they have many limitations: mechanical shot peening has low precision, easily causes surface roughness or damage, and is difficult to adapt to the complex spatial morphology of lattice structures; nanosecond laser shock peening requires the addition of an absorption layer and a constraint layer, which is complex and easily introduces impurities. At the same time, the significant thermal effect may lead to deformation or performance degradation of lattice structure members.
[0004] Picosecond lasers, with their ultrashort pulse width and ultra-high peak power, can achieve near-heat-affected zone processing during impact strengthening, without the need for additional absorption and constraint layers, enabling precise strengthening of localized areas (lattice structure nodes). However, after the lattice structure is additively formed, it is difficult to use ultrafast lasers to perform impact strengthening on each node. Therefore, developing an in-situ interlayer thermal effect of ultrafast lasers to control residual stress in laser additive manufacturing lattice structures, transforming residual tensile stress into high-amplitude residual compressive stress, strengthening microstructure, refining grains, controlling dislocations and defects, improving texture and anisotropy, enhancing surface quality and geometric accuracy, strengthening mechanical properties, and improving durability are of great significance. Summary of the Invention
[0005] To address the problems of stress concentration, porosity, and residual tensile stress at the nodes of existing laser powder bed fused lattice structures, and their tendency to fracture due to stress concentration during actual load-bearing processes, this invention provides a method for improving the durability of additive manufacturing lattice structures through interlayer thermal effects.
[0006] To achieve the above objectives, the present invention provides the following technical solution:
[0007] A method for improving the durability of additively manufactured lattice structures through interlayer thermal effects includes the following steps:
[0008] S1: Use simulation software to construct a stress distribution model of the lattice structure to obtain the weak areas at the nodes of the lattice structure that are prone to stress concentration.
[0009] Based on the initial stress field of the lattice structure, the regions at the nodes of the lattice structure that are prone to stress concentration are identified.
[0010] S2: Model preprocessing and parameter planning: Slice the lattice structure and plan the laser scanning path. Extract and mark the stress concentration areas and failure-prone areas at the nodes identified in S1, and set them as the areas of interlayer thermal effect of picosecond laser.
[0011] Computer-aided design software includes computer-aided design software and Materialise Magics software. Computer-aided design software is used to create a three-dimensional solid geometric model of the sample, while Materialise Magics software is used to obtain the laser additive manufacturing and ultrafast laser scanning processing steps of the three-dimensional solid geometric model and import the processing steps into the laser additive manufacturing equipment.
[0012] S3: Ultrafast laser in-situ thermodynamic additive manufacturing:
[0013] Debugging system, calibrating the coaxial accuracy of additive manufacturing laser and picosecond laser;
[0014] Close the forming chamber, vent the air and introduce inert gas (argon) to maintain the oxygen content in the chamber at 200-400 ppm;
[0015] Additive forming: The continuous laser additive module is activated to melt metal powder layer by layer according to the planned path to form a single-layer matrix with a lattice structure.
[0016] Picosecond laser in-situ strengthening involves converting the laser after the single-layer lattice structure matrix is formed, and using the picosecond laser to induce shock waves and cavitation effects to thermally modify the marked nodal stress concentration areas.
[0017] Continuous cycle continuous laser forming—picosecond laser shock enhancement until the lattice structure is completely formed;
[0018] Continuous laser parameters: laser power 300-450W, spot diameter 60-100μm, scanning speed 600-1200mm / s, scanning spacing 50-80μm. Powder thickness 30-50μm.
[0019] Design parameters for picosecond laser: laser energy 8-12 J / cm² 2 The pulse width is 2ps, the spot diameter is 10-100μm, the laser frequency is 10-1000kHz, the scanning interval is 25%-75% of the spot diameter, and the number of impacts is 2-4.
[0020] Compared with existing technologies, traditional impact strengthening or nanosecond laser impact strengthening easily introduces thermal deformation, surface remelting, or microcracks, making the pillars of the lattice structure prone to warping and resulting in significant differences in dimensional accuracy. Picosecond laser impact strengthening, due to the ultrashort pulse of the picosecond laser, causes almost no thermal diffusion, thus protecting the thin walls of the lattice and achieving better dimensional accuracy. Traditional impact strengthening is difficult to penetrate deep into the interior of the lattice structure, complex curved surfaces, and enclosed cavities. Picosecond lasers, with their micron-level spot size, can target stress concentration areas such as nodes, pillar roots, and hole edges, avoiding structural instability caused by overall impact. This addresses the three major failure issues of stress concentration at nodes, pillar buckling, and shear band initiation, achieving both localized strengthening and overall shape preservation.
[0021] Thermal processing eliminates the need for water, constraint layers, and sacrificial layers, enabling dry processing that avoids residual media, corrosion, or contamination within the lattice. Furthermore, it can be seamlessly integrated with LPBF technology to achieve a unified "additive manufacturing + ultrafast laser thermal processing" solution.
[0022] In current additive manufacturing processes, defects such as incomplete powder fusion, pore aggregation, and microcracks can easily lead to stress concentration at the nodes, making these nodes weak points prone to mechanical failure. During actual load-bearing, the presence of these defects often causes stress concentration at the nodes first. When the stress exceeds the material's yield strength, it triggers the propagation of microcracks at the nodes, ultimately leading to node fracture and lattice structure failure. By integrating ultrafast laser thermodynamics with additive manufacturing, thermal effects are immediately applied to the nodes after the layer-by-layer lattice structure is formed. This suppresses the generation of node defects from multiple dimensions, including microstructure, stress state, and surface quality, thereby reducing stress concentration at the nodes, strengthening weak points, and making the nodes less prone to fracture. This improves the durability and mechanical properties of laser additive manufacturing lattice structures and solves the problem of easy defect initiation and subsequent failure at the nodes of current additive manufacturing lattice structures. Attached Figure Description
[0023] Figure 1 This is a flowchart of the present invention;
[0024] Figure 2 A lattice structure model diagram for an embodiment;
[0025] Figure 3 A schematic diagram illustrating the differentiated process of the lattice structure nodes / rods in an embodiment;
[0026] Figure 4 This is an optical image of the nodal region in Example 1;
[0027] Figure 5 This is an optical image of the nodal region in Example 2;
[0028] Figure 6 This is a residual stress diagram of the block simulated by LPBF forming in Example 2. Detailed Implementation
[0029] The specific technical solution of the present invention will be described with reference to the embodiments. The materials used in the following embodiments are Al-Mg-Sc-Zr alloy powder.
[0030] Example 1
[0031] like Figure 1 The process shown includes the following steps:
[0032] Model preprocessing and parameter planning: for example Figure 2 The lattice structure shown is sliced and laser scanning path is planned. The stress concentration areas and failure-prone areas at the nodes identified in S1 are extracted and marked, and set as the areas of interlayer thermal effect of picosecond laser.
[0033] Computer-aided design software includes computer-aided design software and Materialise Magics software. Computer-aided design software is used to create a three-dimensional solid geometric model of the sample, while Materialise Magics software is used to obtain the laser additive manufacturing and ultrafast laser scanning processing steps of the three-dimensional solid geometric model and import the processing steps into the laser additive manufacturing equipment.
[0034] Debugging system, calibrating the coaxial accuracy of additive manufacturing laser and picosecond laser;
[0035] Close the forming chamber, vent the air and introduce inert gas (argon) to maintain the oxygen content in the chamber at 200-400 ppm;
[0036] Additive forming involves activating a continuous laser additive module to melt metal powder layer by layer according to a planned path, forming a single-layer matrix with a lattice structure.
[0037] Picosecond laser in-situ strengthening involves converting the laser after the single-layer lattice structure matrix is formed, and using the picosecond laser to induce shock waves and cavitation effects to thermally modify the marked nodal stress concentration areas.
[0038] Continuous cycle continuous laser forming—picosecond laser shock enhancement until the lattice structure is completely formed;
[0039] The additive manufacturing continuous laser parameters were designed based on the node dimensions, with a laser power of 400W, a spot diameter of 60μm, a scanning speed of 1000mm / s, and a scanning spacing of 60μm. The powder thickness was 40μm.
[0040] Based on the ablation energy threshold of aluminum alloy, the picosecond laser parameters were designed as follows: laser energy 4 J / cm². 2 The laser spot diameter is 50 μm, the laser frequency is 500 kHz, the line spacing is 50% of the laser spot diameter, and the number of impacts is 2.
[0041] Example 2
[0042] Preparation of lattice structure specimens:
[0043] Model preprocessing and parameter planning: A 3D model of a lattice structure is established, and the model is sliced layer by layer using slicing software;
[0044] The continuous laser parameters of Example 1 are used;
[0045] Close the forming chamber, vent the air and introduce inert gas (argon) to maintain the oxygen content in the chamber at 200-400 ppm;
[0046] Additive manufacturing directly prints the designed lattice structure into shape.
[0047] After the forming chamber cools down, the sample is removed, and then wire cutting technology is used to separate the sample from the substrate.
[0048] Post-processing of the samples includes operations such as grinding, polishing, and etching.
[0049] Unlike Example 1, the picosecond laser interlayer thermal effect was not applied to the nodes of the lattice structure.
[0050] Example 3
[0051] like Figure 3 As shown, the difference from Example 1 is that all rods and nodes of the lattice structure are treated with picosecond lasers. Everything else is the same as in Example 1.
[0052] Example 4
[0053] The difference from Example 1 is that the picosecond laser parameters use a laser energy of 10 J / cm². 2 Everything else is the same as in Example 1.
[0054] Example 5
[0055] Unlike Example 1, the picosecond laser parameters used a laser energy of 0.1 J / cm². 2 Everything else is the same as in Example 1.
[0056] Example 6
[0057] The difference from Example 1 is that the picosecond laser parameters used are a laser energy of 20 J / cm². Everything else is the same as in Example 1.
[0058] Table 1: Bearing Capacity and Explanation of Lattice Structure Nodes under Different Processes in the Examples
[0059] Example Bearing capacity illustrate Example 1 40MPa In Example 1, the defects at the nodes of the lattice structure are reduced, and the residual stress manifests as residual compressive stress, thus alleviating the problem of stress concentration at the nodes. The mechanical properties of the nodes, such as hardness and strength, are improved. Under load, node fracture is reduced, and the service life of the lattice structure is extended. Example 2 20MPa The lattice structure in Example 2 is prone to incomplete fusion and porosity, making it susceptible to thermal cracking. Residual stress manifests as residual tensile stress, and stress concentration is highly likely to occur at the nodes. Under load, the nodes are highly prone to fracture, resulting in a low service life for the lattice structure. Example 3 40MPa Similar to the results of Example 1, and with improved mechanical properties such as strength and hardness of the rods, the time required for forming the lattice structure increased dramatically. Example 4 30MPa In Example 4, the nodes of the formed lattice structure will experience ablation due to the excessively high energy density of the picosecond laser. The material will evaporate, the powder will spread unevenly, and defects such as cracks and pores will easily appear. The stress concentration at the nodes will be aggravated, and the nodes will be more prone to fracture, leading to the failure of the lattice structure. Example 5 25MPa In Example 5, the lattice structure nodes had a low picosecond laser energy density, resulting in minimal thermal effect and yielding similar results to Example 1. However, residual tensile stress was reduced, and hardness and strength were slightly improved. Example 6 10MPa In Example 6, the nodes of the formed lattice structure were ablated due to the picosecond laser energy density being at a severe ablation threshold, resulting in defect initiation and a reduction in load-bearing capacity below the untreated level. The performance of the lattice structure was severely degraded.
[0060] Table 1 shows that compared with Example 2, which did not undergo picosecond laser thermal treatment, Example 1 exhibits significantly improved tissue properties, reduced defects and stress concentration, and a significantly increased load-bearing capacity. The service performance of the lattice structure has been significantly improved, such as... Figure 4 , Figure 5 and Figure 6As shown in Example 3, due to the need for picosecond laser to thermally act on all rods and nodes, although the improvement effect is better than that of Example 1, the time required for lattice structure formation increases sharply, resulting in low efficiency and making this process method unsuitable for production use. Examples 4 and 6 both used picosecond laser energy densities exceeding the ablation threshold of Al-Mg-Sc-Zr alloys. At normal ablation thresholds, although the load-bearing capacity is improved, the resulting ablation phenomenon can cause defects in the nodes during the forming process and may also lead to node fracture, resulting in lattice structure failure. At severely ablated energy densities, the nodes undergo more severe ablation, and defects such as crack initiation occur, causing the load-bearing capacity to drop below the untreated level, and the load-bearing performance of the lattice structure is significantly reduced. Example 5 uses a very low picosecond laser energy density, resulting in an insignificant thermal effect and no significant improvement in node load-bearing capacity.
[0061] This indicates that the present invention significantly improves the microstructure, defects, and mechanical properties of lattice structures manufactured by laser additive manufacturing under the thermal effect of picosecond lasers. However, the improvement of the nodal region of the lattice structure using picosecond lasers with higher and lower energy densities is not significant and may even reduce the performance of the nodal regions.
[0062] It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should be considered as the scope of protection of this invention.
Claims
1. A method for improving the durability of additively manufactured lattice structures through interlayer thermal effects, characterized in that, Includes the following steps: S1: Use simulation software to construct a stress distribution model of the lattice structure to obtain the weak areas at the nodes of the lattice structure that are prone to stress concentration. Based on the initial stress field of the lattice structure, the regions at the nodes of the lattice structure that are prone to stress concentration are identified. S2: Model preprocessing and parameter planning: Slice the lattice structure and plan the laser scanning path. Extract and mark the stress concentration areas and failure-prone areas at the nodes identified in S1, and set them as the areas of interlayer thermal effect of picosecond laser. The laser additive manufacturing and ultrafast laser scanning processes for obtaining the three-dimensional solid geometric model are then introduced into the laser additive manufacturing equipment. S3: Ultrafast laser in-situ thermodynamic additive manufacturing.
2. The method for improving the durability of additively manufactured lattice structures through interlayer thermal effects according to claim 1, characterized in that, The specific process of S3 includes: Debugging system and calibrating the coaxial accuracy of additive manufacturing laser and picosecond laser; Close the forming chamber, exhaust the air and introduce inert gas to maintain the oxygen content in the chamber at 200-400 ppm; Additive forming: The continuous laser additive module is activated to melt metal powder layer by layer according to the planned path to form a single-layer matrix with a lattice structure. Picosecond laser in-situ strengthening involves converting the laser after the single-layer lattice structure matrix is formed, and using the picosecond laser to induce shock waves and cavitation effects to thermally modify the marked nodal stress concentration areas. Continuous cycle continuous laser forming—picosecond laser shock strengthening until the lattice structure is completely formed.
3. The method for improving the durability of additively manufactured lattice structures through interlayer thermal effects according to claim 2, characterized in that, The continuous laser parameters in S3 are as follows: laser power is 300-450W, spot diameter is 60-100μm, scanning speed is 600-1200mm / s, scanning interval is 50-80μm, and powder thickness is 30-50μm.
4. The method for improving the durability of additively manufactured lattice structures through interlayer thermal effects according to claim 2, characterized in that, S3 picosecond laser parameters: laser energy 8-12 J / cm² 2 The pulse width is 2ps, the spot diameter is 10-100μm, the laser frequency is 10-1000kHz, the scanning interval is 25%-75% of the spot diameter, and the number of impacts is 2-4.