A method and system for forming overhanging structures using magnetic field assisted enhanced powder bed laser melting

Abstract

The application discloses a kind of laser melting overhanging structure forming method and system using magnetic field auxiliary enhancement powder bed, method includes: the overhanging angle of overhanging structure is identified, and marked as the overhanging forming section needing magnetic field enhancement;According to the overhanging angle of overhanging forming section, the gradient magnetic field required for the shear stiffness of the powder bed under the enhanced overhanging forming section melt pool is generated, so that the enhanced powder bed resists the shear force of the melt pool of overhanging forming section to flow down, improve the shear strength of powder bed;Using laser scanning system, the powder of overhanging forming section is selected and fused, and printing is completed.The application strengthens the shear stiffness of the powder bed under the overhanging area by magnetic field orientation, provides stable and reliable mechanical support for the melt pool, can effectively resist the shear force generated by the gravity of the melt pool, and improve the forming quality.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and in particular to a method and system for forming laser melting and hanging structures using a magnetic field-assisted reinforced powder bed. Background Technology

[0002] In the traditional laser powder bed melting (LPBF) process, when the suspended structure is formed, the molten metal in the pool will generate a shear force downward along the inclined surface under the action of gravity. The loose powder bed has weak bonding force between particles and low shear strength, making it difficult to effectively resist this shear force. This can easily lead to phenomena such as lateral displacement of powder particles and instability of the molten pool profile, which in turn leads to increased roughness of the suspended surface, reduced dimensional accuracy, edge "nodules", and even cause the overall collapse of the structure.

[0003] Currently, the most important and almost the only effective industrial-grade solution for forming overhanging structures using laser powder bed melting technology is "pre-designing and printing a solid support structure." This is a passive compensation physical solution, the logic of which is: since the loose powder bed under the overhang cannot provide sufficient support, a solid structure with sufficient strength is artificially added at that location to support the molten pool and the upper part. The most important and fundamental drawback of this solution is that, in order to solve a temporary problem caused by "insufficient mechanical properties of the loose powder bed," it introduces a permanent and costly additional manufacturing and post-processing process. This specifically leads to a series of chain of negative effects: (1) waste of materials and energy (2) lengthening and complication of the process chain (3) limited design freedom (4) affecting the quality of the final part. On the other hand, powder functionalization (e.g., mixing a small amount of low-melting-point polymer powder into metal powder or spraying a small amount of binder after powder spreading, using the heat of the laser or a separate heat source to pre-solidify it locally under the overhang area to form a temporary support with a certain strength) will introduce impurity contamination and is not suitable for the preparation of high-performance metal parts.

[0004] To address the challenges of forming suspended structures, existing technologies, besides conventional methods like adding solid support structures and adjusting process parameters, have also developed some magnetic field-assisted additive manufacturing techniques. However, these techniques utilize an alternating magnetic field generated by an electromagnetic coil to act on molten metal droplets, causing them to generate an upward repulsive force to overcome gravity. This allows laser additive manufacturing to be performed in any tilt direction, solving the problem of limited growth direction during in-situ part repair. Examples include application numbers CN202110384494.8, CN20081019700.1, and CN20251149608.1. However, in these existing technologies, the magnetic field acts on molten metal droplets in a melting pool, which differs from the principle and mechanism of this application. Summary of the Invention

[0005] To address the problems existing in the prior art, the purpose of this invention is to provide a method and system for forming laser melting overhanging structures using a magnetic field-assisted powder bed enhancement. In this invention, the magnetic field acts on the powder bed under the molten pool, rather than the molten pool and droplets. This can actively and directionally enhance the shear stiffness of the loose powder bed below the overhanging area, thereby effectively improving the forming accuracy, surface quality, and printing success rate of the overhanging structure with reduced or even no physical support.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] A method for forming laser melting overhang structures using a magnetic field-assisted powder bed reinforcement includes the following steps:

[0008] (1) Based on the three-dimensional model of the part to be formed and its printed layer slice data, identify the overhang structure in the current printing layer, calculate the overhang angle θ of the overhang structure, and mark the overhang structure contour section with an overhang angle θ greater than the preset angle threshold as the overhang forming section that needs magnetic field enhancement.

[0009] (2) Based on the overhang angle θ of the overhang forming section, calculate the gradient magnetic field required to enhance the shear stiffness of the powder bed below the molten pool in the overhang forming section, so that the enhanced powder bed can resist the shear force of the molten pool flowing downward in the overhang forming section; wherein, the gradient magnetic field changes with the powder height, specifically as follows:

[0010]

[0011] In the formula, For powder height Magnetic field strength at that location It is the magnetic susceptibility of the powder particles. The permeability of free space, Let be the density of the molten metal, g be the acceleration due to gravity, and z be the depth of the molten pool. The density of the powder particles. The internal friction angle of the powder;

[0012] (3) After the powder laying of the current printing layer is completed, a control command is sent to the gradient magnetic field generating device to generate a gradient magnetic field at the powder bed formed below the overhanging forming section. This improves the shear strength of the powder bed;

[0013] (4) Use a laser scanning system to selectively melt the powder in the suspended forming section to complete the printing of the current printing layer, and turn off the gradient magnetic field generating device;

[0014] (5) Return to step (1) until the overhang structure is manufactured.

[0015] Furthermore, the preset angle threshold is specifically [35°, 60°].

[0016] Furthermore, the gradient magnetic field generating device is activated before the laser scanning system is activated by a preset time period to complete the powder bed enhancement.

[0017] Furthermore, when a gradient magnetic field is applied at the powder bed At this time, the powder below the suspended forming section is magnetized, and each powder is subjected to an additional magnetic force perpendicular to the bottom. This magnetic force is superimposed on the powder's own gravity in the same direction, which increases the total normal force acting on the powder bed and thus improves the shear strength of the powder bed.

[0018] Furthermore, the gradient magnetic field generating device is an electromagnet with a coil wound around it.

[0019] A laser melting and hanging structure forming system employing magnetic field-assisted powder bed reinforcement includes a control unit, a powder spreading structure, a gradient magnetic field generating device, and a laser scanning system.

[0020] The control unit is used to identify the overhanging structure in each printing layer based on the 3D model of the part to be formed and its printed layer slice data, calculate the overhanging angle θ of the overhanging structure, and mark the overhanging structure contour segments with an overhanging angle θ greater than a preset angle threshold as overhanging forming segments requiring magnetic field reinforcement; and calculate the gradient magnetic field required to enhance the shear stiffness of the powder bed below the molten pool of the overhanging forming segment based on the overhanging angle θ, so that the reinforced powder bed can resist the shear force of the molten pool flowing downward in the overhanging forming segment; wherein, the gradient magnetic field varies with the powder height, specifically as follows:

[0021]

[0022] In the formula, For powder height Magnetic field strength at that location It is the magnetic susceptibility of the powder particles. The permeability of free space, Let be the density of the molten metal, g be the acceleration due to gravity, and z be the depth of the molten pool. The density of the powder particles. The internal friction angle of the powder;

[0023] The powder-laying structure is used to complete the powder laying for each printing layer within the forming cylinder;

[0024] The control unit is also used to send control commands to the gradient magnetic field generating device after the powder is laid.

[0025] The gradient magnetic field generating device is used to generate a gradient magnetic field at the powder bed formed below the overhanging forming section when a control command is received. This improves the shear strength of the powder bed;

[0026] The laser scanning system is used to selectively melt the powder in the overhanging forming section to complete the printing of the current printing layer;

[0027] The control unit is also used to shut down the gradient magnetic field generating device after the current printing layer is completed, and to control the next printing layer until the overhang structure is manufactured.

[0028] Furthermore, the preset angle threshold is specifically [35°, 60°].

[0029] Furthermore, the gradient magnetic field generating device is activated before the laser scanning system is activated by a preset time period to complete the powder bed enhancement.

[0030] Furthermore, when a gradient magnetic field is applied at the powder bed At this time, the powder below the suspended forming section is magnetized, and each powder is subjected to an additional magnetic force perpendicular to the bottom. This magnetic force is superimposed on the powder's own gravity in the same direction, which increases the total normal force acting on the powder bed and thus improves the shear strength of the powder bed.

[0031] Furthermore, the gradient magnetic field generating device is an electromagnet with a coil wound around it.

[0032] Compared with the prior art, the beneficial effects of this invention are:

[0033] (1) Significantly improves the forming quality and accuracy of the overhanging structure: By enhancing the shear stiffness of the powder bed below the overhanging area through magnetic field orientation, a stable and reliable mechanical support is provided for the molten pool, which can effectively resist the shear force generated by the gravity of the molten pool. This directly suppresses phenomena such as molten pool instability, powder displacement and edge "nodules", thereby greatly improving the surface finish of the overhanging surface (such as reducing the roughness Ra value), dimensional accuracy and contour fidelity, so that the overhang angle limit of high-quality unsupported forming can be significantly extended.

[0034] (2) Effectively reduces or even eliminates the use of physical supports, saving material and energy costs: This method fundamentally reduces the reliance on additional physical support structures by enhancing the temporary support capacity of the powder bed itself. This means that a large amount of metal powder material that would otherwise be used for printing supports can be saved, while reducing the energy consumption of laser melting of the support structure. For parts that require complex supports, the benefits of saving materials and energy are particularly prominent.

[0035] (3) Simplify post-processing and improve overall manufacturing efficiency: Due to the reduction or elimination of physical support, the subsequent tedious and time-consuming support removal process (such as wire cutting, grinding, etc.) can be greatly simplified or even omitted. This not only reduces the manpower and equipment costs of post-processing, but more importantly, it significantly shortens the overall delivery cycle of parts from printing to final usability, and improves equipment utilization and production efficiency.

[0036] (4) Releasing design freedom and empowering innovative structure manufacturing: It gets rid of the strong dependence on the addability and removability of physical support, allowing designers to adopt advanced designs such as topology optimization, lattice structure, and complex internal flow channels more freely, to achieve more extreme hanging angles and lighter, more functionally integrated innovative configurations, thus expanding the design boundaries and application potential of laser powder bed melting technology.

[0037] (5) Improved process stability and reliability: Magnetic field enhancement, as an active and controllable online process control method, can dynamically adjust the magnetic field strength according to the suspension angle to achieve adaptive support. This active intervention improves the stability and process window of the suspended structure forming process, reduces the risk of printing failure due to insufficient support, and improves the printing success rate.

[0038] (5) The device is easy to integrate and highly practical: The entire device has a relatively simple structure and is easy to integrate into the bottom of the forming cylinder of existing commercial laser powder bed melting equipment. The control logic is clear and can be realized by synchronizing with the scanning path through software. There is no need to make major changes to the core laser and powder spreading system of the equipment. The modification cost is controllable and it has good prospects for industrial application and promotion. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the laser melting and hanging structure forming system using a magnetic field-assisted enhanced powder bed provided in an embodiment of the present invention;

[0040] Figure 2 This is a schematic flowchart of a laser melting and overhanging structure forming method using a magnetic field-assisted reinforced powder bed provided in an embodiment of the present invention;

[0041] Figure 3 This is a schematic diagram of the state of a cantilever beam manufactured using the present invention;

[0042] Figure 4 This is a schematic diagram showing the state of the I-shaped rail connector manufactured using this invention. Detailed Implementation

[0043] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0044] This invention provides a laser melting and overhanging structure forming system using a magnetic field-assisted enhanced powder bed, such as... Figure 1 As shown, the system includes a laser scanning system 1, a control unit 2, a powder spreading structure (not shown), a gradient magnetic field generating device 3, and a forming cylinder 4. The laser scanning system 1 performs laser scanning and melting, the control unit 2 provides overall control, the powder spreading structure spreads a layer of powder in the forming cylinder 4 after each printing layer is completed for the next layer to be printed, and the gradient magnetic field generating device 3 generates a gradient magnetic field to enhance the shear strength of the powder bed.

[0045] like Figure 2 As shown, this embodiment of the invention also provides a method for forming a laser melting overhang structure using a magnetic field-assisted reinforced powder bed, comprising the following steps:

[0046] (1) Based on the three-dimensional model of the part to be formed 5 and its printing layer slice data, identify the overhang structure in the current printing layer, calculate the overhang angle θ of the overhang structure, and mark the overhang structure contour section with an overhang angle θ greater than the preset angle threshold as the overhang forming section 6 that needs magnetic field enhancement.

[0047] Preset angle threshold θ th It can be optimized according to material properties and process requirements, with a typical value range of 35° to 60°.

[0048] (2) Based on the overhang angle θ of the overhang forming section 6, calculate the gradient magnetic field required to enhance the shear stiffness of the powder bed 7 below the molten pool of the overhang forming section 6, so that the enhanced powder bed 7 can resist the shear force of the molten pool of the overhang forming section 6 flowing downward.

[0049] Specifically, the first step is to calculate the total shear force generated by the molten pool. Based on the stress model of the molten pool on an inclined surface established by scholars, the shear force of the molten pool is... In the formula Let g be the density of the molten pool metal, g be the gravitational acceleration, and z be the depth of the molten pool.

[0050] Next, the shear strength that the powder bed can provide is calculated, according to the Mohr-Coulomb failure criterion. In the formula To enhance the strength of the powder bed against shear failure, For powder cohesion, For normal stress, The powder's internal friction angle is denoted as . Since the powder bed is not pre-sintered and the powder used is only tens to hundreds of micrometers in size, the cohesive force is relatively small. In this invention, gravity plays a dominant role, and the powder cohesive force is negligible; therefore, it can be modified as follows: .

[0051] Height is h pThe magnetic force experienced by powder particles on a powder bed in a gradient magnetic field is V p It refers to the volume of the powder particles. It is the magnetic susceptibility of the powder particles. The permeability of free space, Let be the magnetic field strength, and ∇ be the gradient.

[0052] In engineering practice, to ensure reliability, the total shear force generated by the molten pool is... This is considered as the shear component required for the powder bed to resist the flow of the molten pool, i.e. normal stress The sum of the powder's own gravity and the additional magnetic force generated by the gradient magnetic field is considered for a powder bed with a height of h. p The powder has a gravity of , Given the powder particle density and a powder porosity of 50%, the following derivation can be made:

[0053]

[0054] Solving the above formula yields:

[0055] .

[0056] (3) After the powder laying of the current printing layer is completed, a control command is sent to the gradient magnetic field generating device 3 to generate a gradient magnetic field at the powder bed formed below the hanging forming section. This improves the shear strength of the powder bed.

[0057] The gradient magnetic field generating device 3 is activated before the laser scanning system by a preset time period to enhance the powder bed. The magnetic field duration covers the entire laser scanning process of the suspended section. By adjusting parameters such as the input current, the magnetic field strength and gradient distribution can be controlled in real time, thereby achieving active and precise control over the magnitude of the magnetic force on the powder particles.

[0058] The gradient magnetic field generating device 3 precisely generates a vertically downward controllable gradient magnetic field at the powder bed directly below the suspended forming section. The powder below the suspended forming section is magnetized, and each powder particle experiences an additional downward magnetic force. This magnetic force is superimposed on the powder's own weight in the same direction, increasing the total normal force acting on the powder bed. Macroscopically, this manifests as a significant increase in the normal compressive stress on the powder bed. According to the principles of powder mechanics, the increase in normal pressure directly and proportionally increases the shear strength of the powder bed. Therefore, the shear stiffness and stability of the powder bed 7 in this region are directionally and locally enhanced. Figure 1As shown, the powder in powder bed 7 (small black dots) is more compact and has greater shear stiffness, while the powder in the rest of the powder (large black dots) is looser and has less shear stiffness.

[0059] Among them, the gradient magnetic field generating device 3 can be an electromagnet with a coil wound around it, thereby generating... Magnetic field.

[0060] (4) Use a laser scanning system to selectively melt the powder in the suspended forming section, complete the printing of the current printing layer, and turn off the gradient magnetic field generating device.

[0061] Under the continuous action of the magnetic field, the laser beam 8 of the laser scanning system is controlled to selectively melt the suspended forming section according to the preset scanning path. At this time, the shear resistance of the powder bed below has been significantly enhanced by the magnetic field, which can effectively resist the shear stress generated by the molten metal in the pool along the inclined surface under the action of gravity, avoid the lateral displacement of powder particles, and thus ensure the stability of the molten pool contour and the clear forming boundary.

[0062] (5) Return to step (1) until the overhang structure is manufactured.

[0063] Specifically, the forming cylinder 4 descends by one printing layer thickness, the powder spreading mechanism spreads a new layer of powder, and then steps 1 to 4 are repeated until the entire overhang structure is manufactured.

[0064] Based on the above description, the function of each module in the molding system is confirmed as follows:

[0065] The control unit 2 is used to identify the overhanging structure in each printing layer based on the 3D model of the part to be formed and its printing layer slice data, calculate the overhanging angle θ of the overhanging structure, and mark the overhanging structure contour segment with an overhanging angle θ greater than a preset angle threshold as an overhanging forming segment requiring magnetic field reinforcement; and calculate the gradient magnetic field required to enhance the shear stiffness of the powder bed below the molten pool of the overhanging forming segment based on the overhanging angle θ, so that the reinforced powder bed can resist the shear force of the molten pool flowing downward in the overhanging forming segment; wherein, the gradient magnetic field varies with the powder height, specifically as follows:

[0066]

[0067] In the formula, For powder height Magnetic field strength at that location It is the magnetic susceptibility of the powder particles. The permeability of free space, Let be the density of the molten metal, g be the acceleration due to gravity, and z be the depth of the molten pool. The density of the powder particles. The internal friction angle of the powder;

[0068] The powder-laying structure is used to complete the powder laying for each printing layer within the forming cylinder;

[0069] The control unit 2 is also used to send control commands to the gradient magnetic field generating device after the powder is laid, thereby generating a gradient magnetic field at the powder bed formed below the overhanging forming section. This improves the shear strength of the powder bed;

[0070] Laser scanning system 1 is used to selectively melt the powder in the overhanging forming section to complete the printing of the current printing layer;

[0071] The control unit 2 is also used to shut down the gradient magnetic field generating device after the current printing layer is completed, and to control the next printing layer until the overhang structure is manufactured.

[0072] The gradient magnetic field generating device 3 and the control unit 2 are powered by the power supply 9.

[0073] It is worth noting that in the embodiments of the above system, the various units and modules included are only divided according to functional logic, but are not limited to the above division, as long as the corresponding functions can be achieved; in addition, the specific names of each functional unit are only for easy distinction between each other and are not used to limit the scope of protection of the present invention.

[0074] The embodiments described above are merely illustrative. The modules described as separate components may or may not be physically separate, and the components shown as modules may or may not be physical modules; that is, they may be located in one place or distributed across multiple network modules. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art will clearly understand that each implementation can be achieved using software plus necessary general-purpose hardware platforms, or it can be implemented solely through hardware, as long as the function or purpose can be achieved.

[0075] The following experiments will verify the invention:

[0076] Example 1: Figure 3 As shown, the example is an Inconel 718 alloy cantilever beam (a typical cantilever structure) with an inclination angle of 55°, a length of 50 mm, and a thickness of 1.5 mm.

[0077] Equipment and Materials: An electromagnet array is integrated at the bottom of the forming cylinder. Inconel 718 powder (particle size 15-53μm) is used. Basic process parameters: laser power 280W, scanning speed 850mm / s, layer thickness 30μm.

[0078] Comparative example: When printed to a length of approximately 20mm, the beam exhibited significant downward deflection and rough edges, ultimately failing to complete the printing process.

[0079] Implementation steps:

[0080] (1) Control unit sets θ th =40°, and the cantilever beam profile was identified as a suspended section from the slice data.

[0081] (2) After each layer of powder is laid, 30ms before the laser scans the beam outline, the control unit drives the corresponding electromagnet to activate, generating a downward gradient magnetic field of 0.35T, which lasts for 70ms.

[0082] (3) The magnetic field causes the powder particles to be subjected to a downward magnetic force, which, combined with gravity, increases the normal stress, thereby significantly improving the shear stiffness of the powder bed.

[0083] (4) The laser beam scans and the molten pool is stably formed on the reinforced powder bed.

[0084] (5) Repeat the above process layer by layer to complete the manufacturing of the entire cantilever beam.

[0085] Results: A complete and straight cantilever beam was successfully printed. The formed beam has accurate dimensions, a smooth cantilever surface, and no collapse or deformation. The measured surface roughness Ra of the cantilever beam was reduced by more than 40% compared to the control model.

[0086] Example 2: Figure 4 As shown, the example is a small chemical-grade rail connector for railway tracks.

[0087] Equipment and Materials: An electromagnet array is integrated at the bottom of the forming cylinder. 316L stainless steel powder (particle size 15-50μm) is used. Basic process parameters: laser power 300W, scanning speed 800mm / s, layer thickness 50μm.

[0088] Comparative example: Printing was performed using the same 316L powder and basic process parameters, but without magnetic field assistance. When printing reached the suspended part of the upper flange of the I-shaped structure, due to the loose powder support below and insufficient shear stiffness, the molten metal in the pool seeped downwards under gravity, resulting in severe slag and nodule formation on the lower surface of the upper flange.

[0089] Implementation steps:

[0090] (1) Overhanging area identification: The control unit sets the tilt angle threshold θ th =35°, and from the slice data, the lower surface of the upper flange and the transition area of ​​the web of the I-shaped section were identified as overhanging sections. These areas have no physical support below them during the forming process and rely entirely on the powder bed for support.

[0091] (2) Gradient magnetic field application: After each layer of powder is laid, before the laser beam begins to scan the overhanging section, the control unit dynamically drives the corresponding electromagnet array at the bottom of the forming cylinder to activate based on the position information of the overhanging area of ​​the current layer, generating a gradient magnetic field B with a vertical downward direction and an intensity of 0.30T. The magnetic field intensity is gradient distributed in the depth direction of the powder bed to ensure that the powder particles are subjected to a stable and downward magnetic force.

[0092] (3) Powder bed shear reinforcement: Under the action of a gradient magnetic field, 316L stainless steel powder particles (ferromagnetic) are subjected to an additional magnetic force perpendicularly downward. This magnetic force is in the same direction as the particle's own gravity G and is superimposed. The normal compressive stress inside the powder bed increases significantly, thereby greatly improving the shear stiffness of the powder bed in the powder spreading plane, so that the originally loose powder layer forms a stable support structure.

[0093] (4) Laser scanning and forming: The laser beam scans along the planned path. Since the powder bed below has enhanced shear resistance, it can effectively resist the downward seepage tendency and lateral shear force of the molten metal pool caused by gravity. The molten pool maintains a stable shape, and the upper flange of the I-shaped section is clearly formed without collapse or slag.

[0094] (5) Layer-by-layer repetition: Repeat the steps of powdering, overhanging area identification, selective magnetic field application and laser scanning layer by layer until the entire I-shaped rail structure is manufactured.

[0095] Results: The I-shaped rail structure with precise dimensions and clear outline was successfully printed. The lower surface of the upper flange of the formed part is smooth and flat, without defects such as nodules or slag. The measured surface roughness Ra is reduced by more than 45% compared with the comparison sample. The transition between the web and the flange is smooth, without the generation of microcracks.

[0096] The above embodiments demonstrate that the present invention effectively solves a common problem in this field by focusing on the overhanging structure and directionally enhancing the shear resistance of the powder bed below it.

[0097] It should be understood that the embodiments and descriptions above are only the principles, main features and advantages of the present invention. Various changes and modifications can be made to the present invention without departing from the spirit and scope of the invention, and all such changes and modifications fall within the protection scope of the present invention.

Claims

1. A method for forming laser melting and overhanging structures using a magnetic field-assisted powder bed reinforcement, characterized in that, Includes the following steps: (1) Based on the three-dimensional model of the part to be formed and its printed layer slice data, identify the overhang structure in the current printing layer, calculate the overhang angle θ of the overhang structure, and mark the overhang structure contour section with an overhang angle θ greater than the preset angle threshold as the overhang forming section that needs magnetic field enhancement. (2) Based on the overhang angle θ of the overhang forming section, calculate the gradient magnetic field required to enhance the shear stiffness of the powder bed below the molten pool in the overhang forming section, so that the enhanced powder bed can resist the shear force of the molten pool flowing downward in the overhang forming section; wherein, the gradient magnetic field changes with the powder height, specifically as follows: , In the formula, For powder height Magnetic field strength at that location It is the magnetic susceptibility of the powder particles. The permeability of free space, Let be the density of the molten metal, g be the acceleration due to gravity, and z be the depth of the molten pool. The density of the powder particles. The internal friction angle of the powder; (3) After the powder laying of the current printing layer is completed, a control command is sent to the gradient magnetic field generating device to generate a gradient magnetic field at the powder bed formed below the overhanging forming section. This improves the shear strength of the powder bed; (4) Use a laser scanning system to selectively melt the powder in the suspended forming section to complete the printing of the current printing layer, and turn off the gradient magnetic field generating device; (5) Return to step (1) until the overhang structure is manufactured.

2. The laser melting and overhanging structure forming method using a magnetic field-assisted enhanced powder bed according to claim 1, characterized in that, The preset angle threshold is specifically [35°, 60°].

3. The laser melting and overhanging structure forming method using a magnetic field-assisted reinforced powder bed according to claim 1, characterized in that, The gradient magnetic field generating device is activated before the laser scanning system is activated by a preset time period to complete the powder bed enhancement.

4. The laser melting and overhanging structure forming method using a magnetic field-assisted reinforced powder bed according to claim 1, characterized in that, When a gradient magnetic field is applied to the powder bed At this time, the powder below the suspended forming section is magnetized, and each powder is subjected to an additional magnetic force perpendicular to the bottom. This magnetic force is superimposed on the powder's own gravity in the same direction, which increases the total normal force acting on the powder bed and thus improves the shear strength of the powder bed.

5. The laser melting and overhanging structure forming method using a magnetic field-assisted reinforced powder bed according to claim 1, characterized in that, The gradient magnetic field generating device is an electromagnet with a coil wound around it.

6. A laser melting and overhanging structure forming system employing a magnetic field-assisted enhanced powder bed, characterized in that, Includes a control unit, a powder spreading structure, a gradient magnetic field generating device, and a laser scanning system. The control unit is used to identify the overhanging structure in each printing layer based on the 3D model of the part to be formed and its printed layer slice data, calculate the overhanging angle θ of the overhanging structure, and mark the overhanging structure contour segments with an overhanging angle θ greater than a preset angle threshold as overhanging forming segments requiring magnetic field reinforcement; and calculate the gradient magnetic field required to enhance the shear stiffness of the powder bed below the molten pool of the overhanging forming segment based on the overhanging angle θ, so that the reinforced powder bed can resist the shear force of the molten pool flowing downward in the overhanging forming segment; wherein, the gradient magnetic field varies with the powder height, specifically as follows: , In the formula, For powder height Magnetic field strength at that location It is the magnetic susceptibility of the powder particles. The permeability of free space, Let be the density of the molten metal, g be the acceleration due to gravity, and z be the depth of the molten pool. The density of the powder particles. The internal friction angle of the powder; The powder-laying structure is used to complete the powder laying for each printing layer within the forming cylinder; The control unit is also used to send control commands to the gradient magnetic field generating device after the powder is laid. The gradient magnetic field generating device is used to generate a gradient magnetic field at the powder bed formed below the overhanging forming section when a control command is received. This improves the shear strength of the powder bed; The laser scanning system is used to selectively melt the powder in the overhanging forming section to complete the printing of the current printing layer; The control unit is also used to shut down the gradient magnetic field generating device after the current printing layer is completed, and to control the next printing layer until the overhang structure is manufactured.

7. The laser melting and overhanging structure forming system using a magnetic field-assisted enhanced powder bed according to claim 6, characterized in that, The preset angle threshold is specifically [35°, 60°].

8. The laser melting and overhanging structure forming system using a magnetic field-assisted enhanced powder bed according to claim 6, characterized in that, The gradient magnetic field generating device is activated before the laser scanning system is activated by a preset time period to complete the powder bed enhancement.

9. The laser melting and overhanging structure forming system using a magnetic field-assisted enhanced powder bed according to claim 6, characterized in that, When a gradient magnetic field is applied to the powder bed At this time, the powder below the suspended forming section is magnetized, and each powder is subjected to an additional magnetic force perpendicular to the bottom. This magnetic force is superimposed on the powder's own gravity in the same direction, which increases the total normal force acting on the powder bed and thus improves the shear strength of the powder bed.

10. The laser melting and overhanging structure forming system using a magnetic field-assisted enhanced powder bed according to claim 6, characterized in that, The gradient magnetic field generating device is an electromagnet with a coil wound around it.

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