A cascaded modulation laser powder bed additive manufacturing method and system

Abstract

The application discloses a kind of cascade modulation laser powder bed additive manufacturing method and system, belong to metal additive manufacturing technical field, including laser emission and pre-shaping module, first stage digital beam modulation module, first dynamic zoom relay module, second stage digital beam modulation module, second dynamic zoom projection module, scanning and focusing module and powder bed forming module in turn along optical path.It is generated single patterning spot according to unit shape by first stage digital beam modulation module, and the physical size of the spot is adjusted by first dynamic zoom relay module;Second stage digital beam modulation module copies and arranges the adjusted unit pattern into two-dimensional array, and the total projection area of the array is adjusted by second dynamic zoom projection module.By the cascade of two-stage modulation and two-stage zoom, the stepless continuous adjustment of dot matrix structure unit shape, unit size and array span is realized, and complex patterns can be formed by single exposure, suitable for gradient dot matrix and multi-scale composite structure additive manufacturing.

Description

Technical Field

[0001] This application relates to the field of metal additive manufacturing technology, and in particular to a cascaded modulated laser powder bed additive manufacturing method and system. Background Technology

[0002] Laser powder bed fusion (L-PBF) technology manufactures three-dimensional parts by melting metal powder layer by layer. When manufacturing lightweight components with periodic lattice structures (such as crystal lattices and honeycomb structures), traditional L-PBF uses a single Gaussian spot for point-by-point scanning, which has inherent defects such as low efficiency, thermal stress concentration, and difficulty in forming complex and fine structures.

[0003] To improve efficiency, existing technologies attempt to perform beam shaping:

[0004] Single SLM shaping: Uses a single spatial light modulator to shape the light spot into a simple shape (flat-top, ring) or a static array. However, the physical dimensions of the generated pattern are fixed, resulting in poor flexibility. To change the feature size or array size, optical elements must be replaced, making flexible manufacturing impossible. Multi-beam technology: Uses diffractive optical elements (DOEs) for beam splitting or multiple lasers for parallel processing. The beam arrangement and intensity distribution generated by DOEs are fixed and cannot be changed in real-time through programming. Multi-laser systems are expensive, and the coordinated control between beams is complex. Dual-laser system: Uses two sets of lasers to process in different areas; while it can partition the area, it does not achieve the complex patterned dynamic projection of a single beam.

[0005] In summary, current technologies lack an optical system capable of dynamically generating complex two-dimensional patterns with real-time programmable dimensions and arrangement in a single exposure, and directly applying them to powder bed melting. This severely restricts the design freedom and manufacturing efficiency of high-performance lattice structures (especially those with gradient and multi-scale features). Summary of the Invention

[0006] This invention addresses the problems existing in the background technology by proposing a cascaded modulated laser powder bed additive manufacturing method and system. It overcomes the shortcomings of existing laser powder bed fusion (L-PBF) technology in manufacturing lattice structures, such as low efficiency, poor flexibility, and difficulty in manufacturing gradient lattices with variable feature sizes. The invention provides a cascaded modulated laser powder bed additive manufacturing system and method capable of forming complex two-dimensional patterns in a single exposure, with both the pattern unit and overall size dynamically adjustable in real time. By cascading modulation of two stages of SLM (Spark Laser Modulation), the beam shape and arrangement are given unlimited programming capabilities; further, two stages of dynamic zoom provide unlimited adjustment capabilities for its size. This combination achieves, for the first time in the L-PBF field, truly "arbitrary pattern, arbitrary size" single-exposure forming.

[0007] To solve the technical problem, the technical solution of the present invention is as follows: A method for additive manufacturing of cascaded modulated laser powder bed, the method comprising: S1: Obtain the pattern parameters of the current forming layer, the pattern parameters including unit feature information and array coverage information; S2: Based on the unit feature information, calculate the first modulation parameters required for the first-stage beam modulation and the first zoom parameters required for the first-stage zoom; based on the array coverage information, calculate the second modulation parameters required for the second-stage beam modulation and the second zoom parameters required for the second-stage zoom. S3: Configure two-stage spatial light modulators according to the first modulation parameters and the second modulation parameters respectively, and configure two-stage dynamic zoom modules according to the first zoom parameters and the second zoom parameters respectively. The two-stage dynamic zoom modules include: a first-stage zoom and a second-stage zoom. S4: After the laser beam passes through the first-level modulation, the first dynamic zoom relay module, the second-level modulation, and the second dynamic zoom projection module in sequence, it outputs a light spot array on the powder bed surface that meets the requirements of the current layer pattern parameters, and melts the powder to form the current layer; S5: Repeat steps S1 to S4 to manufacture layer by layer until a three-dimensional part is obtained.

[0008] Furthermore, in step S1, the pattern parameters are derived from slice data of the target three-dimensional dot matrix model, the unit feature information includes the basic geometry of the unit and the target unit size D_unit, and the array coverage information includes the target array arrangement and the target array coverage size D_array.

[0009] Further, in step S2, the first modulation parameter is the first phase map Φ1 loaded onto the first spatial light modulator, which is calculated using an iterative algorithm based on the basic geometry of the unit; the first zoom parameter is the first zoom parameter Z1 of the first dynamic zoom relay module, which is calculated using an optical model based on the target unit size D_unit; the second modulation parameter is the second phase map Φ2 loaded onto the second spatial light modulator, which is calculated based on the target array arrangement; the second zoom parameter is the second zoom parameter Z2 of the second dynamic zoom projection module, which is calculated using an optical model based on the target array coverage size D_array.

[0010] Furthermore, step S2 also includes: adjusting the laser power setting value P based on the change in projected area calculated by the second zoom parameter Z2, so as to maintain a constant effective energy density on the powder bed surface.

[0011] Further, step S3 includes: driving the first dynamic zoom relay module to adjust to the first zoom parameter Z1 state and loading the first phase map Φ1 onto the first spatial light modulator; driving the second dynamic zoom projection module to adjust to the second zoom parameter Z2 state and loading the second phase map Φ2 onto the second spatial light modulator; and setting the output power of the laser beam emission to the laser power setting value P.

[0012] Further, in step S4, the process of the laser beam sequentially undergoing first-level modulation, first-level zoom, second-level modulation, and second-level zoom specifically includes: after being homogenized by the laser emission and pre-shaping module, the laser beam is incident on the first-level digital beam modulation module; after being modulated by the first spatial light modulator loaded with the first phase map Φ1, a patterned light spot of a single target geometry is output; after the patterned light spot is adjusted in physical size by the first dynamic zoom relay module, a unit pattern with the target unit size D_unit is output; the unit pattern is incident on the second spatial light modulator loaded with the second phase map Φ2, and after modulation, an array pattern is output that is copied and arranged into a preset two-dimensional periodic array; after the array pattern is adjusted in projection area by the second dynamic zoom projection module, a final light spot array with the target array coverage size D_array is output to the scanning and focusing module.

[0013] Furthermore, in step S5, when manufacturing the gradient lattice structure, the pattern parameters obtained in step S1 for different molding layers are set to different values, and the method dynamically switches the process parameters between layers.

[0014] A cascaded modulated laser powder bed additive manufacturing system includes, in sequence along the optical path: a laser emission and pre-shaping module, a first-stage digital beam modulation module, a first dynamic zoom relay module, a second-stage digital beam modulation module, a second dynamic zoom projection module, a scanning and focusing module, and a powder bed forming module; The first-stage digital beam modulation module is connected to the output end of the laser emission and pre-shaping module. The first-stage digital beam modulation module includes a first spatial light modulator and a first reflector. The first reflector reflects the beam output by the laser emission and pre-shaping module to the first spatial light modulator. The first dynamic zoom relay module's input end is connected to the output end of the first-level digital beam modulation module, and the first dynamic zoom relay module includes a first motorized zoom lens group. The second-stage digital beam modulation module is connected to the output end of the first dynamic zoom relay module. The second-stage digital beam modulation module includes a second mirror, a third mirror, a second spatial light modulator, and a fourth mirror. The beam output from the first dynamic zoom relay module is guided to the second spatial light modulator by the second mirror and the third mirror in sequence. The beam modulated by the second spatial light modulator is then incident on the fourth mirror. The second dynamic zoom projection module's incident end is connected to the output end of the second-stage digital beam modulation module, and the second dynamic zoom projection module includes a second motorized zoom lens group. The scanning and focusing module's input end is connected to the output end of the second dynamic zoom projection module, and the scanning and focusing module includes a galvanometer and a field lens; The powder bed forming module is located at the exit end of the scanning and focusing module.

[0015] Furthermore, the system also includes a central integrated control system, which is electrically connected to the laser emission and pre-shaping module, the first spatial light modulator, the first motorized zoom lens group, the second spatial light modulator, the second motorized zoom lens group, the scanning and focusing module, and the powder bed forming module, respectively.

[0016] This application has the following advantages: By using "software-defined" phase maps and zoom parameters, stepless continuous manufacturing from micron-level fine dot arrays to millimeter-level macro dot arrays can be achieved on the same equipment without stopping the machine to replace any hardware, solving the problem of insufficient flexibility of traditional solutions.

[0017] By transforming point-by-point scanning of dozens or even hundreds of points into a single projection exposure containing the same number of feature patterns, the forming efficiency can be improved by one to two orders of magnitude, making it particularly suitable for the manufacturing of large-scale dot matrix structures.

[0018] The programmable light intensity distribution of the liquid crystal spatial light modulator helps to achieve more uniform energy input, reduce spatter and porosity caused by overheating at the center of the Gaussian spot, improve the morphology of the melting channel, and reduce residual stress.

[0019] This provides new technological means for the design and manufacturing of functional integrated components such as performance gradient lattices and biomimetic multi-scale structures. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the overall system structure provided in an embodiment of the present invention; Figure 2 This is a general flowchart of the method of the present invention; Figure 3 Slicing a three-dimensional lattice structure; Figure 4 For the unit shape and the target array shape; Figure 5 The unit shape and corresponding phase diagram; Figure 6 The target array shape and corresponding phase diagram are shown.

[0022] Explanation of icon numbers: 100 - Laser emission and pre-shaping module; 101 - Fiber laser; 102 - Collimator; 103 - Beam homogenizer; 200 - First-stage digital beam modulation module; 201 - First reflector; 202 - First spatial light modulator; 300 - First dynamic zoom relay module; 301 - First motorized zoom lens group; 302 - Fixed lens; 400 - Second-stage digital beam modulation module; 401 - Second reflector; 402 - Third reflector; 4 03-Second spatial light modulator; 404-Fourth reflecting mirror; 500-Second dynamic zoom projection module; 501-Second electric zoom lens group; 502-Fixed lens; 600-Scanning and focusing module; 601-Scanning galvanometer; 602-Field lens; 700-Powder bed forming module; 701-Protective gas unit; 702-Powder spreading roller; 703-Dust purification unit; 704-Forming cylinder; 705-Powder supply cylinder; 800-Central integrated control system. Detailed Implementation

[0023] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0024] Example 1: The cascaded modulated laser powder bed additive manufacturing system described in this embodiment is as follows: Figure 1As shown, its optical path is divided into the following modules according to function.

[0025] The laser emission and pre-shaping module 100 includes a fiber laser 101, a collimator 102, and a beam homogenizer 103. The fiber laser 101 generates continuous or pulsed laser light in the near-infrared band. After being collimated by the collimator 102, it is incident on the beam homogenizer 103, outputting a collimated beam with uniform intensity distribution, which is then incident on the first-stage digital beam modulation module 200. The laser light output from the fiber laser 101 has good coherence. Combined with the beam homogenizer 103, it achieves intensity homogenization while maintaining coherence, thus meeting the coherence requirements of the phase-type spatial light modulator for the incident light wavefront.

[0026] The first-stage digital beam modulation module 200 includes a first reflector 201 and a first phase-type spatial light modulator 202. The first reflector 201 reflects the incident uniform beam to the first spatial light modulator 202. The first spatial light modulator 202 loads a first phase map calculated by the central integrated control system 800 based on the shape of the target dot matrix unit, and shapes the incident light wavefront through pure phase modulation to form a single real image spot of the desired geometry in the Fourier domain.

[0027] The first dynamic zoom relay module 300 consists of a first motorized zoom lens group 301 and a fixed lens 302 forming a 4-f relay optical path. Its input terminal receives the unit pattern output by the first-stage digital beam modulation module 200. The central integrated control system 800 continuously adjusts the imaging size of the unit pattern on the output surface by changing the focal length of the first motorized zoom lens group 301. The first dynamic zoom relay module 300 adopts a 4-f optical structure. By changing the focal length of the first motorized zoom lens group 301, it continuously adjusts the imaging size of the unit pattern while keeping the output image plane position unchanged. The adjustment range is determined by the numerical aperture of the optical system and the pixel size of the spatial light modulator, enabling stepless adjustment of the unit size from the micrometer level to the millimeter level. Similarly, the second dynamic zoom projection module 500 adjusts the total area of ​​the array projection while keeping the image plane position unchanged.

[0028] The second-stage digital beam modulation module 400 includes a second reflector 401, a third reflector 402, a second phase-type spatial light modulator 403, and a fourth reflector 404. The unit pattern output from the first dynamic zoom relay module 300 is sequentially guided to the second spatial light modulator 403 via the second reflector 401 and the third reflector 402. The second spatial light modulator 403 loads a second phase map calculated by the central integrated control system 800 based on the target dot matrix arrangement, and performs secondary modulation on the incident unit pattern, replicating and arranging it into a regular N×M two-dimensional array. The modulated array beam exits after being deflected by the fourth reflector 404. The pixel resolution of the second spatial light modulator 403 determines the upper limit of the array replication quantity. The central integrated control system 800 automatically calculates the phase map based on the target array arrangement to ensure that the period of the replicated array matches the SLM pixel size, avoiding aliasing or a decrease in diffraction efficiency.

[0029] The second dynamic zoom projection module 500 consists of a second motorized zoom lens group 501 and a fixed lens 502 forming a 4-f relay optical path. Its input terminal receives the array pattern output by the second-stage digital beam modulation module 400. The central integrated control system 800 continuously adjusts the total area of ​​the entire array pattern projected onto the powder bed surface by changing the focal length of the second motorized zoom lens group 501.

[0030] The scanning and focusing module 600 includes a scanning galvanometer 601 and a field lens 602, which guide and focus the scaled beam array onto the forming plane of the powder bed forming module 700.

[0031] The powder bed forming module 700 is a standard laser powder bed melting and forming chamber, including a protective gas unit 701, a powder spreading roller 702, a dust purification unit 703, a forming cylinder 704, and a powder supply cylinder 705.

[0032] The central integrated control system 800 is electrically connected to all the above modules and includes a phase map calculation unit, motion control card and laser controller. It is used to receive 3D model slice data, calculate and output the command sequence for controlling each module in real time, so as to realize full-process synchronization and coordination.

[0033] Example 2: like Figure 2 As shown, this embodiment uses the fabrication of a lattice structure with a gradient change along the Z-direction (construction direction) as an example to illustrate the forming method of the system.

[0034] Step 1: Data preparation; Slice the target 3D raster model (see...) Figure 3), obtain the unit shape, target unit size D_unit(k), and target array coverage size D_array(k) of the current forming layer k (see Figure 4 ).

[0035] Step 2: Dynamic calculation layer by layer; The central integrated control system 800 performs the following calculations: a) Based on the cell shape of the current layer, use an iterative algorithm to calculate the first phase map Φ1(k) required for the first spatial light modulator (see...). Figure 5 ); b) Based on the array arrangement of the current layer, calculate the second phase map Φ2(k) required for the second spatial light modulator (see...). Figure 6 ); c) Based on the target unit size D_unit(k), calculate the first zoom parameter Z1(k) required by the first dynamic zoom relay module using the optical model; d) Based on the target array coverage size D_array(k), calculate the second zoom parameter Z2(k) required by the second dynamic zoom projection module using the optical model; e) Based on the projected area determined by the second zoom parameter Z2(k), adjust the laser power setting value P(k) to maintain a constant effective energy density on the powder bed surface. The laser power setting value P(k) is calculated according to the formula P(k)=P_base×(A(k) / A_base), where A(k) is the projected area of ​​the current layer, and P_base and A_base are the baseline process parameters to maintain a constant energy density per unit area.

[0036] Step 3: System reconfiguration; After the powder is applied and before exposure begins, the central integrated control system 800 drives the first dynamic zoom relay module to adjust to the Z1(k) state and drives the second dynamic zoom projection module to adjust to the Z2(k) state; loads the first phase map Φ1(k) onto the first spatial light modulator and loads the second phase map Φ2(k) onto the second spatial light modulator; and sets the laser output power to P(k).

[0037] After the system completes all parameter configurations, the central integrated control system 800 sends synchronous trigger signals to the laser and scanning galvanometer 601 to ensure that exposure is performed only after both modulation and zoom modules are in a steady state. Step 4: Exposure and shaping; The laser beam is controlled to emit light. After passing through the first-level digital beam modulation, the first-level zoom, the second-level digital beam modulation, and the second-level zoom in sequence, a two-dimensional pattern array is formed, in which the unit size and the array coverage size both meet the design requirements of the current layer. The array is then projected onto a designated area of ​​the powder bed by a scanning galvanometer, melting the powder to form the current layer structure.

[0038] Step 5: Lamination manufacturing; The powder-laying mechanism lays down the next layer of powder. The system reads the process parameters of layer k+1 and repeats steps 1 to 4, building up layer by layer until the 3D part is manufactured. When manufacturing the gradient lattice structure, the target unit size D_unit and / or the target array coverage size D_array of different layers are set to different values. The system automatically switches process parameters between layers to achieve an automated cycle of "powder laying-parameter update-exposure". When there are significant changes in D_unit or D_array between adjacent layers, the central integrated control system 800 automatically matches the laser power and scanning strategy according to the preset process database to ensure the quality of metallurgical bonding between layers.

[0039] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0040] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for additive manufacturing of cascaded modulated laser powder bed, characterized in that, The method includes: S1: Obtain the pattern parameters of the current forming layer, the pattern parameters including unit feature information and array coverage information; S2: Based on the unit feature information, calculate the first modulation parameters required for the first-stage beam modulation and the first zoom parameters required for the first-stage zoom; based on the array coverage information, calculate the second modulation parameters required for the second-stage beam modulation and the second zoom parameters required for the second-stage zoom. S3: Configure two-stage spatial light modulators according to the first modulation parameters and the second modulation parameters respectively, and configure two-stage dynamic zoom modules according to the first zoom parameters and the second zoom parameters respectively. The two-stage dynamic zoom modules include: a first-stage zoom and a second-stage zoom. S4: After the laser beam passes through the first-level modulation, the first dynamic zoom relay module, the second-level modulation, and the second dynamic zoom projection module in sequence, it outputs a light spot array on the powder bed surface that meets the requirements of the current layer pattern parameters, and melts the powder to form the current layer; S5: Repeat steps S1 to S4 to manufacture layer by layer until a three-dimensional part is obtained.

2. The cascaded modulated laser powder bed additive manufacturing method according to claim 1, characterized in that, In step S1, the pattern parameters are derived from slice data of the target three-dimensional dot matrix model, the unit feature information includes the basic geometry of the unit and the target unit size D_unit, and the array coverage information includes the target array arrangement and the target array coverage size D_array.

3. The cascaded modulated laser powder bed additive manufacturing method according to claim 2, characterized in that, In step S2, the first modulation parameter is the first phase map Φ1 loaded onto the first spatial light modulator, which is calculated using an iterative algorithm based on the basic geometry of the unit; the first zoom parameter is the first zoom parameter Z1 of the first dynamic zoom relay module, which is calculated using an optical model based on the target unit size D_unit; the second modulation parameter is the second phase map Φ2 loaded onto the second spatial light modulator, which is calculated based on the target array arrangement; the second zoom parameter is the second zoom parameter Z2 of the second dynamic zoom projection module, which is calculated using an optical model based on the target array coverage size D_array.

4. The cascaded modulated laser powder bed additive manufacturing method according to claim 3, characterized in that, The S2 step further includes: adjusting the laser power setting value P based on the change in projected area calculated by the second zoom parameter Z2, so as to maintain a constant effective energy density on the powder bed surface.

5. The cascaded modulated laser powder bed additive manufacturing method according to claim 4, characterized in that, Step S3 includes: driving the first dynamic zoom relay module to adjust to the first zoom parameter Z1 state and loading the first phase map Φ1 onto the first spatial light modulator; driving the second dynamic zoom projection module to adjust to the second zoom parameter Z2 state and loading the second phase map Φ2 onto the second spatial light modulator; and setting the output power of the laser beam emission to the laser power setting value P.

6. The cascaded modulated laser powder bed additive manufacturing method according to claim 5, characterized in that, In step S4, the process of the laser beam sequentially undergoing first-level modulation, first-level zoom, second-level modulation, and second-level zoom specifically includes: after being homogenized by the laser emission and pre-shaping module, the laser beam is incident on the first-level digital beam modulation module; after being modulated by the first spatial light modulator loaded with the first phase map Φ1, a patterned light spot of a single target geometry is output; after the patterned light spot is adjusted in physical size by the first dynamic zoom relay module, a unit pattern with the target unit size D_unit is output; the unit pattern is incident on the second spatial light modulator loaded with the second phase map Φ2, and after modulation, an array pattern is output that is copied and arranged into a preset two-dimensional periodic array; after the array pattern is adjusted in projection area by the second dynamic zoom projection module, a final light spot array with the target array coverage size D_array is output to the scanning and focusing module.

7. The cascaded modulated laser powder bed additive manufacturing method according to claim 1, characterized in that, In step S5, when manufacturing the gradient lattice structure, the pattern parameters obtained in step S1 for different molding layers are set to different values, and the method dynamically switches the process parameters between layers.

8. A cascaded modulated laser powder bed additive manufacturing system, characterized in that, It includes, in sequence along the optical path: a laser emission and pre-shaping module, a first-stage digital beam modulation module, a first dynamic zoom relay module, a second-stage digital beam modulation module, a second dynamic zoom projection module, a scanning and focusing module, and a powder bed forming module; The first-stage digital beam modulation module is connected to the output end of the laser emission and pre-shaping module. The first-stage digital beam modulation module includes a first spatial light modulator and a first reflector. The first reflector reflects the beam output by the laser emission and pre-shaping module to the first spatial light modulator. The first dynamic zoom relay module's input end is connected to the output end of the first-level digital beam modulation module, and the first dynamic zoom relay module includes a first motorized zoom lens group. The second-stage digital beam modulation module is connected to the output end of the first dynamic zoom relay module. The second-stage digital beam modulation module includes a second mirror, a third mirror, a second spatial light modulator, and a fourth mirror. The beam output from the first dynamic zoom relay module is guided to the second spatial light modulator by the second mirror and the third mirror in sequence. The beam modulated by the second spatial light modulator is then incident on the fourth mirror. The second dynamic zoom projection module's incident end is connected to the output end of the second-stage digital beam modulation module, and the second dynamic zoom projection module includes a second motorized zoom lens group. The scanning and focusing module's input end is connected to the output end of the second dynamic zoom projection module, and the scanning and focusing module includes a galvanometer and a field lens; The powder bed forming module is located at the exit end of the scanning and focusing module.

9. The cascaded modulated laser powder bed additive manufacturing system according to claim 8, characterized in that, The system further includes a central integrated control system, which is electrically connected to the laser emission and pre-shaping module, the first spatial light modulator, the first motorized zoom lens group, the second spatial light modulator, the second motorized zoom lens group, the scanning and focusing module, and the powder bed forming module.

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