A laser cladding 3D / 4D printing system and method

Abstract

The application provides a laser cladding 3D / 4D printing system and method, comprising the following steps: S1, constructing a three-dimensional model of a to-be-printed piece, and slicing the three-dimensional model to generate a two-dimensional interface graph of each layer of printing; S2, using a first laser to melt additive manufacturing material of a current layer to form a cladding layer; S3, using a second laser to perform micro-shaping on the surface of the cladding layer, first performing micro-shaping on the rough and hole defect area of the surface of the cladding layer, then performing point heat source irradiation on the surface of the cladding layer to eliminate residual stress of the cladding layer; S4, repeating steps S2-S3 to complete the additive manufacturing process of each layer to obtain a printed piece. The application eliminates the residual stress of the cladding layer of the laser 3D / 4D printed workpiece, the hole of the interface-surface, the uneven roughness and the powder agglomeration accumulation problem by performing ultrafast laser shaping on the cladding layer in the laser 3D / 4D printing process, thereby improving the quality of the laser 3D / 4D printed piece.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser additive manufacturing, and specifically relates to a laser cladding 3D / 4D printing system and method. Background Art

[0002] Laser 3D / 4D printing (such as selective laser sintering (SLS) and selective laser melting (SLM), as advanced additive manufacturing technologies, has demonstrated unique advantages in industry, medicine, and scientific research. These advantages include: ① High-precision and complex structure manufacturing capabilities. For example, laser beam focusing diameters can reach 20 μm-100 μm, enabling micron-level resolution (for example, metal printing accuracy can reach ± ​​0.05 mm), making it suitable for manufacturing complex cavities, honeycomb structures, or topology-optimized components that are difficult to process using traditional methods; ② Material diversity, such as support for a variety of materials, including metals (titanium alloys, aluminum alloys, nickel-based high-temperature alloys), ceramics, and polymers (such as nylon PA12). Direct metal forming is a core advantage that distinguishes it from other 3D printing technologies; ③ No molds are required and rapid iteration is required, going directly from digital models to physical parts, eliminating the mold development process and shortening the new product development cycle (for example, the production time of automotive prototypes can be reduced by 70%); ④ High material utilization. Powder bed technology can achieve an unmelted material recovery rate of over 95%, significantly reducing the loss of expensive materials (such as titanium alloys).

[0003] Although laser 3D / 4D printing has many advantages, it also has many obvious defects, such as: ① Residual stress defects. During the laser cladding 3D / 4D printing process, the non-uniform thermal cycle induced by the high-energy laser can lead to thermoelastic stress, phase change stress, warping deformation and interface failure; ② Surface roughness and unevenness defects. Due to the spheroidization effect or step effect and the influence of powder adhesion, the surface of the laser cladding 3D / 4D printed workpiece will appear rough and uneven; ③ Interface-surface hole defects, including keyhole pores formed due to the instability of the molten pool dynamics, unfused holes formed due to insufficient laser energy density, and powder agglomeration and accumulation due to poor powder fluidity. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems in the prior art of large residual stress in the cladding layer of laser 3D / 4D printed workpieces and holes and roughness on the interface-surface of the cladding layer.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A laser cladding 3D / 4D printing method comprises the following steps:

[0007] S1. Build a 3D model of the part to be printed based on its parameters, slice the 3D model, and generate a 2D interface diagram for each printed layer.

[0008] S2, using the first laser to melt the additive manufacturing material of the current layer and form a cladding layer;

[0009] S3. Micro-shaping the surface of the cladding layer using a second laser. First, the surface roughness and hole defect areas of the cladding layer are micro-shaped by adjusting the process parameters of the second laser. Then, the emission power of the second laser is adjusted to irradiate the surface of the cladding layer with a point heat source to eliminate residual stress in the cladding layer. The process parameters for micro-shaping the surface roughness and hole defect areas of the cladding layer by the second laser are adjusted based on the optical information of the cladding layer captured by the holographic camera and the surface roughness and hole defect information of the cladding layer acquired in real time by the stress wave emitted by the pulse generator.

[0010] S4. Repeat steps S2-S3 to complete the additive manufacturing process for each layer until a printed part is obtained.

[0011] Furthermore, a holographic camera is used to obtain a dynamic hologram of the surface of the cladding layer, which is analyzed by a spectrometer to calculate the arithmetic mean roughness parameters of the surface of the cladding layer. Combined with the stress wave fluctuation signal obtained by the stress wave sensor, a roughness joint evaluation model for dual-modal detection is established to calculate the comprehensive roughness value of the surface of the cladding layer. The surface roughness, hole requirements and corresponding mechanical properties of the cladding layer are judged through the correlation mechanism of detection data and parameter adjustment, as well as the real-time feedback and closed-loop control process to adjust the process parameters of the second laser in real time, thereby completing real-time laser processing correction and ultrafast laser micro-shaping of the defective areas on the surface of the cladding layer.

[0012] Furthermore, in step S3, the emission power of the second laser for performing point heat source irradiation on the surface of the cladding layer is adjusted according to the residual stress information on the surface of the cladding layer obtained in real time by the X-ray stress detection device.

[0013] Furthermore, the X-ray stress detection device includes an X-ray generator, an X-ray detector and an X-ray measurement recorder. The X-ray generator emits X-rays to the surface of the cladding layer, the X-ray detector detects the change information of the X-ray diffraction peak position in the surface area of ​​the cladding layer, and the X-ray measurement recorder measures and records the diffraction angle in real time. The real-time diffraction angle data is converted and processed by an industrial computer to obtain the residual stress information on the surface of the cladding layer.

[0014] Furthermore, steps S2, S3, and S4 are performed in a vacuum heating chamber, and the pressure and temperature inside the vacuum heating chamber are controlled in real time by a vacuum pumping device and a heating device.

[0015] In addition, the application also provides a laser cladding 3D / 4D printing system for the laser cladding 3D / 4D printing method, comprising an industrial computer, a laser 3D / 4D printing mechanism, an ultrafast laser shaping mechanism, a holographic camera, a pulse generator, a stress wave sensor, a spectrometer, an X-ray stress detection device and a processing platform for carrying a printed part; the laser 3D / 4D printing mechanism emits first laser for melting additive manufacturing material to form a cladding layer; the ultrafast laser shaping mechanism emits second laser for shaping the cladding layer; the holographic camera is electrically connected with the spectrometer, and the laser 3D / 4D printing mechanism, the ultrafast laser shaping mechanism, the pulse generator, the stress wave sensor, the spectrometer and the X-ray stress detection device are electrically connected with the industrial computer.

[0016] Further, the ultrafast laser shaping mechanism comprises an ultrafast laser, and a first mirror, a half-wave plate, a polarization beam splitter, a spatial light modulator, a 4F optical information processing assembly, a second mirror and a laser probe arranged in sequence along a laser emission light path of the ultrafast laser.

[0017] Further, a flip mirror is arranged on the light path between the 4F optical information processing assembly and the second mirror, so that a branch light path which can be incident into the spectrometer is generated on the light path.

[0018] Further, the laser cladding 3D / 4D printing system further comprises a vacuum heating cavity, and the laser processing head of the laser 3D / 4D printing mechanism, the laser probe of the ultrafast laser shaping mechanism, the holographic camera, the pulse generator, the stress wave sensor, the X-ray stress detection device and the processing platform are all arranged in the vacuum heating cavity in a vacuum sealed manner.

[0019] Compared with the prior art, the application has the following beneficial effects:

[0020] (1) The application eliminates the residual stress, interface-surface holes, uneven roughness and powder agglomeration of the cladding layer of the laser 3D / 4D printed workpiece by shaping the cladding layer with ultrafast laser during the laser 3D / 4D printing process, thereby improving the quality of the laser 3D / 4D printed part; and the shaping of the surface roughness and hole defects of the cladding layer is performed first, and then the elimination of the residual stress of the cladding layer is performed during the ultrafast laser shaping process, so that the residual stress can be improved by the action of the ultrafast laser during the shaping of the surface roughness and hole defects of the cladding layer, thereby the energy for eliminating the residual stress of the cladding layer can be reduced, and the production cost can be reduced.

[0021] (2) The application utilizes the optical information of the cladding layer taken by a holographic camera and the fluctuation signal of stress wave in a combined manner to detect the surface roughness and hole defects of the cladding layer on line and in situ, and utilizes X-ray to detect the residual stress of the cladding layer on line and in situ, and according to the detection results, the local selective superfast laser shaping of the cladding layer is carried out, which not only improves the efficiency and accuracy of the cladding layer shaping, but also further reduces the production cost.

[0022] The application will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a structural schematic diagram of the laser cladding 3D / 4D printing system of the application;

[0024] Figure 2 is a working principle diagram of the laser cladding 3D / 4D printing method of the application.

[0025] BRIEF DESCRIPTION OF DRAWINGS 1, industrial computer; 2, superfast laser; 3, first reflecting mirror, 4, half-wave plate; 5, polarization beam splitter; 6, spatial light modulator; 7, first lens; 8, first laser reflecting mirror; 9, spatial filter; 10, second laser reflecting mirror; 11, second lens; 12, flip mirror; 13, third lens; 14, spectrometer; 15, second reflecting mirror; 16, laser probe; 17, holographic camera; 18, pulse generator; 19, X-ray generator; 20, X-ray detector; 21, X-ray measurement recorder; 22, laser processing head; 23, protective gas inlet mechanism; 24, light path scanning mechanism; 25, printing laser generator; 26, feeding system; 27, printed part; 28, object table; 29, horizontal rotating table; 30, vertical rotating table, 31, bottom support table; 32, molten pool; 33, cladding layer; 34, pressure sensor; 35, temperature sensor; 36, vacuum pumping device; 37, heating device. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0027] In the description of the present application, it needs to be understood that the terms "center", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0028] In the description of the present application, it needs to be understood that the terms "installation", "connection", "connection" should be understood broadly, for example, it can be fixed connection, it can also be detachable connection, it can also be in contact connection or integral connection; for those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0029] The terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more features; in the description of the present application, unless otherwise stated, the meaning of "multiple" is two or more.

[0030] As shown in Figure 1 and Figure 2 The embodiment of the present application provides a laser cladding 3D / 4D printing method, which comprises the following steps:

[0031] S1, according to the parameters of the to-be-printed part, a three-dimensional model of the to-be-printed part is constructed, and the three-dimensional model is sliced to generate a two-dimensional interface graph of each layer of printing;

[0032] S2, using the first laser to melt the additive manufacturing material of the current layer and form a cladding layer 33;

[0033] S3, using the second laser to micro-finish the surface of the cladding layer 33, first adjusting the process parameters of the second laser to micro-finish the surface roughness and hole defect area of the cladding layer 33, and then adjusting the emission power of the second laser to irradiate the surface of the cladding layer 33 with a point heat source, to eliminate the residual stress of the cladding layer 33;

[0034] S4, repeating steps S2-S3 to complete the additive manufacturing process of each layer until the printed part is obtained.

[0035] In the embodiment, the superfast laser shaping is performed on the cladding layer 33 during the laser 3D / 4D printing process to eliminate the residual stress, interface-surface holes, uneven roughness and powder agglomeration accumulation of the cladding layer of the laser 3D / 4D printed workpiece, thereby improving the quality of the laser 3D / 4D printed workpiece. In the superfast laser shaping process, the surface roughness and hole defects of the cladding layer 33 are first shaped, and then the residual stress of the cladding layer 33 is eliminated. In this way, the superfast laser in the process of shaping the surface roughness and hole defects of the cladding layer 33 can improve part of the residual stress, thereby reducing the energy of the subsequent residual stress elimination of the cladding layer 33 and reducing the production cost.

[0036] As a specific embodiment, step S1 specifically includes: obtaining parameters of the to-be-printed workpiece, such as size, shape, material, etc., using the obtained parameters to construct a three-dimensional model of the to-be-printed workpiece by computer-aided design software, and obtaining plastic mechanics parameters, elastic mechanics parameters, yield strength mechanics parameters, etc. of the to-be-printed workpiece to optimize the superfast laser shaping process parameters, and store the optimized superfast laser shaping process parameters in the industrial computer 1 as the reference target parameters for the subsequent superfast laser shaping process of the cladding layer 33. After the construction of the three-dimensional model is completed, the three-dimensional model is subjected to slicing operation. Slicing is to decompose the three-dimensional model into a series of plane layers, and each slice represents a two-dimensional interface graph of a printing operation on the layer. For each plane layer, the computer software generates an additive manufacturing path according to the parameters of the to-be-printed workpiece and the characteristics of the material, and each additive manufacturing path specifies the movement of the laser on each layer to achieve the required shape and structure.

[0037] As a specific embodiment, step S2 specifically includes: the industrial computer 1 sends an instruction to the feeding system 26 to send the additive manufacturing material (i.e. thin layer powder) of the current layer to the laser processing head 22, and at the same time, the industrial computer 1 sends a laser instruction to the laser 3D / 4D printing mechanism, which is transmitted to the laser processing head 22 through the light path scanning mechanism 24 and emits high-energy first laser to "sinter" the thin layer powder on the bottom layer and gradually form the cladding layer 33.

[0038] Optimally, during the process of feeding the additive manufacturing material from the feeding system 26 to the laser processing head 22, inert gas is sent into the laser processing head 22 through the protective gas inlet mechanism 23 to prevent the thin layer powder from being oxidized during the laser 3D / 4D printing process.

[0039] In some embodiments, in the above step S3, the process parameters of the second laser for micro-shaping the surface roughness and hole defect area of the cladding layer 33 can be adjusted according to the optical information of the cladding layer 33 taken by the holographic camera 17 and the surface roughness and hole defect information of the cladding layer 33 obtained by the stress wave generator 18 in real time.

[0040] Specifically, the holographic camera 17 and the pulse generator 18 are placed near the area of the cladding layer 33 close to the molten pool 32, the holographic camera 17 takes the optical information of the cladding layer 33, and the optical signals taken are processed by the spectrometer 14 and transmitted to the industrial computer 1 to obtain the fringe pattern (i.e. dynamic hologram) of the surface of the cladding layer 33, so as to detect and analyze the hole distribution and surface roughness of the cladding layer 33 in real time; at the same time, the pulse generator 18 emits stress waves to the defect area on the surface of the cladding layer 33, the stress waves enter the detection site, and a series of changes such as refraction and diffuse scattering are generated in the defect area on the surface of the cladding layer 33 with a certain roughness and holes, the changed stress wave fluctuation signals are received by the stress wave sensor attached to the holographic camera 17 and transmitted to the industrial computer 1, and the fluctuation signals of the surface roughness and hole defects of the cladding layer 33 processed by the detector and the optical signals and dynamic hologram processed by the spectrometer 14 are received by the industrial computer 1, and the fluctuation signals are processed by the detector, and the surface roughness, hole requirements and corresponding mechanical properties of the cladding layer 33 are judged by the correlation mechanism of detection data and parameter adjustment and the real-time feedback and closed-loop control process, so as to adjust the micro-shaping process parameters of the industrial computer 1 transmitted to the ultrafast laser shaping mechanism, so as to complete the mathematical mapping of roughness quantization and threshold setting and laser parameter adjustment, realize the closed loop of detection-adjustment-verification, and finally complete the real-time laser processing correction and ultrafast laser micro-shaping of the defect area on the surface of the cladding layer 33.

[0041] By adjusting the appropriate ultrafast laser parameters, the protruding substances in the cladding layer 33 can be dispersed and detached instantaneously, and the particle groups agglomerated on the surface of the cladding layer 33 can also be dispersed, so that the interface-surface of the cladding layer 33 of the printed part 27 has better surface flatness; in addition, the ultrafast laser can also play a role of secondary polishing on the rough surface of the cladding layer 33, so as to finally obtain a flat surface of the laser cladding 3D / 4D printed cladding layer interface-surface without holes and with lower roughness. The cladding layer 33 with surface roughness greater than the set threshold value is micro-shaped by the ultrafast laser with adjusted process parameters until the industrial computer 1 detects the surface roughness of the cladding layer 33 in the laser cladding 3D / 4D printing process to be less than the set threshold value.

[0042] In the embodiment, the laser cladding layer 33 with a surface roughness greater than a set threshold is micro-finished by using an ultrafast laser to adjust the process parameters. A correlation mechanism is introduced by combining detection data and parameter adjustment, including roughness quantification and threshold setting, and mathematical mapping of laser parameter adjustment. The roughness quantification and threshold setting include obtaining a dynamic hologram of the surface of the laser cladding layer 33 by using a holographic camera 17, analyzing the surface fringe pattern by using a spectrometer 14, calculating the arithmetic average roughness parameter Ra of the surface of the laser cladding layer 33, and combining the fluctuation signal of the stress wave sensor (the reflection / scattering intensity of the stress wave on the rough surface is positively correlated with the roughness) to establish a dual-mode detection roughness joint evaluation model.

[0043] The average roughness parameter Ra is calculated as follows:

[0044] ;

[0045] In the formula, M and N are the number of points taken on the plane, x j and y i are the horizontal and vertical coordinates of the position of the points taken on the plane, and h is the average height of all point values on the reference surface.

[0046] The formula for calculating the comprehensive roughness value of the roughness joint evaluation model is as follows:

[0047] ; in the formula, is a weight coefficient, wherein , is the amplitude variation rate of the stress wave.

[0048] In the embodiment, the topography analysis of the holographic camera 17 and the mechanical property detection of the stress wave are combined through the synergistic innovation of dual-mode detection to form an “optical-mechanical” composite detection system. Compared with the single CCD camera or pulsed laser scheme used in the prior art, the detection accuracy is improved by at least 40%, and the roughness detection error calculated by the dual-mode detection is less than 0.05 μm.

[0049] The general industrial standard for the surface roughness of laser cladding 3D / 4D printed parts is as follows: ① ordinary mirror surface processing level: roughness of 0.4-0.8 μm; ② clearer mirror surface processing level: roughness of 0.3-0.4 μm; ③ high-quality mirror surface processing level: roughness reduced to 0.05-0.3 μm; and ④ super-high standard mirror surface processing level: roughness less than 0.05 μm.

[0050] The holographic camera 17 scans the plane of a single cladding layer 33 to obtain the horizontal and vertical coordinate data of all the points in the plane of the single cladding layer 33 and transmits it to the industrial computer 1. The average roughness parameter Ra is calculated using the above formula. Combined with the mechanical properties of stress waves, the comprehensive roughness value of the cladding layer 33 is calculated and processed using the roughness joint evaluation model. This is used as the measured roughness value of the surface of the cladding layer 33. If the measured roughness value exceeds a set threshold (for example, 0.4 μm), the industrial computer 1 sends a command to the ultrafast laser shaping mechanism to perform micro-shaping on the surface of the cladding layer 33. The ultrafast laser shaping mechanism then performs impact scanning on the cladding layer 33 with a femtosecond ultrafast laser.

[0051] Specifically, the laser parameters of the ultrafast laser shaping mechanism are adjusted according to the measured roughness. The mathematical mapping of the laser parameter adjustment includes a power adjustment model and energy density calculation. The power adjustment model includes setting a power adjustment formula based on the linear relationship between the roughness value and the laser energy:

[0052] ;

[0053] In the formula is the reference power (such as ), k is the adjustment coefficient (such as 20 W / μm), R is the measured roughness, R th is the threshold value (e.g. 0.4 μm). th When , the power increases linearly with the roughness.

[0054] The energy density calculation is performed using the relationship between the pulse energy and power of the ultrafast laser, specifically:

[0055]

[0056] In the formula is the pulse width (e.g. 50 fs), f rep For the repetition frequency (such as 100 kHz), by adjusting P and , control the energy density within the range of 5-10 J / cm² (experiments have verified that this range can effectively eliminate roughness without damaging the material).

[0057] Preferably, the embodiment adopts a real-time feedback and closed-loop control process to perform ultrafast laser shaping on the surface roughness and hole defects of the cladding layer 33. Specifically, the real-time feedback and closed-loop control process includes data acquisition, parameter pre-adjustment, and real-time correction. The data acquisition includes: the holographic camera 17 acquires the surface morphology of the cladding layer 33 at a certain rate (for example, 1000 fps), the stress wave sensor synchronously acquires the corresponding high-frequency fluctuation signal (for example, 1 MHz fluctuation signal), and the industrial computer 1 calculates the comprehensive roughness value in real time. The parameter pre-adjustment includes an LSTM neural network trained based on historical data to predict the optimal laser parameters (such as power and scanning speed) corresponding to the current roughness, for example: when Ra = 0.6 μm, the predicted power is 16 W and the scanning speed is 200 mm / s; when Ra = 0.8 μm, the predicted power is 20 W and the scanning speed is 150 mm / s. The real-time correction includes verifying the roughness change after each shaping by secondary detection. If the residual roughness R res >0.15R th , then start the secondary adjustment, and the adjustment step is 30% of the initial value.

[0058] Further, the secondary detection of the above-mentioned roughness change includes a zoned ultrafast shaping process after detecting the surface roughness and hole defects of the cladding layer 33, which specifically includes a defect region intelligent division strategy and a combination of spatial grid and dynamic mask. The defect region intelligent division strategy includes a partition criterion based on defect type and density and density clustering. The defect classification includes distinguishing the roughness region (hologram fringe is dense, and stress wave dispersion is obvious) and the hole region (hologram dark spot, and stress wave attenuation is severe) through the gray distribution of the hologram and the stress wave spectrum analysis. The density clustering includes clustering the defect point cloud by using the DBSCAN algorithm (i.e., a density-based clustering algorithm). Specifically, the high-density area (defect point spacing < 50 μm) is divided into a “severe defect area” and is impacted point by point by using high-energy laser (energy density 8-10 J / cm²); the medium-density area (defect point spacing 50-100 μm) is divided into a “general defect area” and is scanned and shaped by using medium energy (5-8 J / cm²); and the low-density area (defect point spacing > 100 μm) is divided into a “slight defect area” and is polished by using low energy (3-5 J / cm²).

[0059] The space grid combined with the dynamic mask includes grid division and dynamic mask generation. Specifically, the grid division includes dividing the surface of the cladding layer 33 into 100x100 pm grid units, and each unit is divided according to the defect parameters (roughness, hole number); the dynamic mask generation includes generating a laser mask matched with the defect division through a spatial light modulator (SLM); specifically, a circular mask with a diameter of 1.5 times the diameter of the hole is generated for the hole region to ensure complete coverage of the defect; a linear scanning mask is generated for the rough region, and the scanning line spacing is 1 / 2 of the roughness wavelength (such as 25 pm when the roughness wavelength is 50 pm).

[0060] In the embodiment, a linear mapping formula of roughness and laser power and an energy density calculation model are established by a quantitative parameter adjustment model to realize accurate regulation and control of the parameters; and a clustering division algorithm based on defect density and type is established by intelligent division and dynamic mask, and a "division-parameter" shaping is realized in combination with an SLM mask generation technology, which can improve the defect elimination efficiency by at least 60% compared with the uniform parameter processing in the prior art.

[0061] In some other embodiments, in the step S3, the emission power of the second laser for point heat source irradiation on the surface of the cladding layer 33 is adjusted according to the residual stress information of the surface of the cladding layer 33 obtained in real time by the X-ray stress detection device.

[0062] Specifically, the X-ray stress detection device includes an X-ray generator 19, an X-ray detector 20, and an X-ray measurement recorder 21; after the shaping of the defect area with rough holes on the surface of the cladding layer 33 is completed, the X-ray generator 19 emits X-rays to the surface of the cladding layer 33, the X-ray detector 20 detects the change information of the X-ray diffraction peak position of the surface area of the cladding layer 33, the X-ray measurement recorder 21 measures and records the diffraction angle in real time, and the real-time diffraction angle data is converted and processed by the industrial computer 1 to obtain the residual stress information of the surface of the cladding layer 33, which includes the size and distribution information of the residual stress of the surface area of the cladding layer 33. The industrial computer 1 sends parameter adjustment information to the ultrafast laser shaping mechanism according to the residual stress information of the surface of the cladding layer 33, and the ultrafast laser shaping mechanism adjusts the emission power of the ultrafast laser according to the parameter adjustment information to complete the point heat source irradiation with different heat on the cladding layer 33 of the printed part. The irradiation of the local point heat source causes a small plastic deformation on the surface of the cladding layer 33, which not only can offset the tensile stress of a certain depth on the surface of the laser 3D / 4D printed part and introduce a residual compressive stress field, but also can effectively improve the mechanical properties of the laser 3D / 4D printed part.

[0063] In an optimized implementation, both the laser printing and cladding layer shaping processes in this embodiment are performed within a sealed vacuum heating chamber, with the pressure and temperature within the vacuum heating chamber controlled in real time by a vacuum pump 36 and a heating device 37. The high vacuum environment of the vacuum heating chamber not only prevents the presence of oxides or other impurities at the interface between cladding layers 33 and within individual cladding layers 33, which could affect the fatigue strength and mechanical properties of the printed part, but the heating device 37 within the high vacuum environment also provides a temperature-raising environment for laser cladding 4D printing, particularly for laser 4D printing of certain shape memory alloys.

[0064] In addition, the embodiment of the present invention also provides a laser cladding 3D / 4D printing system, such as Figure 1 As shown, it specifically includes an industrial computer 1, a laser 3D / 4D printing mechanism, an ultrafast laser shaping mechanism, a holographic camera 17, a pulse generator 18, a stress wave sensor, a spectrometer 14, an X-ray stress detection device and a processing platform for carrying a printed part 27; the laser 3D / 4D printing mechanism emits a first laser to melt the additive manufacturing material to form a cladding layer 33; the ultrafast laser shaping mechanism emits a second laser to shape the cladding layer 33; the holographic camera 17 is electrically connected to the spectrometer 14, and the laser 3D / 4D printing mechanism, the ultrafast laser shaping mechanism, the pulse generator 18, the stress wave sensor, the spectrometer 14, and the X-ray stress detection device are all electrically connected to the industrial computer 1.

[0065] In some embodiments, the laser 3D / 4D printing mechanism includes a laser processing head 22, a printing laser generator 25 and an optical path scanning mechanism 24. The laser processing head 22 contains powder material for additive manufacturing. The laser processing head 22 is located directly above the processing platform. The printing laser generator 25 is electrically connected to the industrial computer 1. The optical path scanning mechanism 24 is located on the emission light path of the printing laser generator 25, and allows the laser emitted by the printing laser generator 25 to be incident on the laser processing head 22.

[0066] Optimally, the laser processing head 22 is connected to a feeding system 26 for adding material to the laser processing head 22 in real time; further optimized, the laser processing head 22 is also connected to a protective gas intake mechanism 23 for introducing an inert protective gas into the laser processing head 22, and the inert protective gas introduced can be but is not limited to argon with a concentration greater than 99.999%; the feeding system 26 and the protective gas intake mechanism 23 are both electrically connected to the industrial computer 1.

[0067] In some other embodiments, the ultrafast laser shaping mechanism comprises an ultrafast laser 2, and a first mirror 3, a half-wave plate 4, a polarization beam splitter 5, a spatial light modulator 6, a 4F optical information processing assembly, a second mirror 15 and a laser probe 16 arranged in sequence along a laser emission light path of the ultrafast laser 2; the ultrafast laser 2 is electrically connected with the industrial computer 1. The 4F optical information processing assembly comprises a first lens 7, a first laser mirror 8, a spatial filter 9, a second laser mirror 10 and a second lens 11 arranged in sequence along the laser emission light path. In operation, the laser emitted by the ultrafast laser 2 is reflected by the first mirror 3, passes through the half-wave plate 4 and the polarization beam splitter 5 (the angle of the half-wave plate 4 can be adjusted to adjust the laser energy), enters the spatial light modulator 6, the spatial light modulator 6 loads a hologram to modulate the phase of light, forms an ultrafast laser beam with high and short pulses, and passes through a 4F optical information processing assembly. In the process of the 4F optical information processing assembly, in order to exclude the influence of zero-order light on processing, the spatial filter 9 is placed at the focal point of the first lens 7 to block the zero-order light and present the image (the image after Fourier transform) of the spatial light modulator 6 on the processing plane, and the generated ultrafast laser passes through the second mirror 15 and enters the laser probe 16 to emit a laser beam to act on the surface area of the cladding layer 33 of the laser 3D / 4D printed part.

[0068] Specifically, by adjusting the lens spacing in the 4F optical information processing assembly (for example, the first lens F = 500 mm and the second lens F = 500 mm), the spot diameter can be continuously adjusted in the range of 20-100 μm, for example, a 20 μm spot is used for a single-point impact with an energy density of 10 J / cm² for a severely defective area, and a 50 μm spot is used for linear scanning with an energy density of 6 J / cm² for a general defective area.

[0069] In a preferred embodiment, a flip mirror 12 is arranged on the light path between the 4F optical information processing assembly and the second mirror 15, so that a branch light path that can enter the spectrometer 14 is generated on the light path, and a third lens 13 is arranged between the flip mirror 12 and the spectrometer 14; the flip mirror 12 between the 4F optical information processing assembly and the second mirror 15 is used to introduce part of the laser into the spectrometer 14 to monitor the plasma spectrum in real time during the shaping process and verify the partition processing effect (for example, the change in the intensity of the characteristic spectral line of the element of the cladding layer 33 reflects the surface flatness).

[0070] In an optional embodiment, the machining platform is a five-axis compound linkage machining platform, which specifically comprises a bottom support table 31, a five-axis linkage rotating platform, and a carrier table 28. The five-axis linkage rotating platform is supported on the bottom support table 31, and the carrier table 28 is installed on the five-axis linkage rotating platform. The five-axis linkage rotating platform drives the carrier table 28 to rotate in the horizontal plane and the vertical plane by means of a horizontal rotating table 29 and a vertical rotating table 30, so as to adjust the relative position relationship between the printed part 27 on the carrier table 28 and the laser machining head 22, the laser probe 16, the holographic camera 17, the pulse generator 18, the stress wave sensor, and the X-ray stress detection device.

[0071] In a preferred embodiment, the laser cladding 3D / 4D printing system further comprises a vacuum heating cavity. The laser machining head 22 of the laser 3D / 4D printing mechanism, the laser probe 16 of the ultrafast laser shaping mechanism, the holographic camera 17, the pulse generator 18, the stress wave sensor, the X-ray stress detection device, and the machining platform are all arranged in the vacuum heating cavity in a vacuum-sealed manner. Optionally, the vacuum heating cavity is provided with a temperature sensor 35 and a pressure sensor 34. The vacuum heating cavity is connected with a vacuumizing device 36 and a heating device 37. The temperature sensor 35, the pressure sensor 34, the vacuumizing device 36, and the heating device 37 are all connected with the industrial computer 1. The temperature sensor 35 and the pressure sensor 34 detect the temperature and the pressure inside the vacuum heating cavity, respectively. According to the detection results, the vacuumizing device 36 and the heating device 37 are used to adjust the pressure and the temperature inside the vacuum heating cavity in real time. The high-vacuum environment of the vacuum heating cavity can effectively avoid the existence of oxides or other impurities in the interface between the cladding layer 33 and the cladding layer 33 and in a single cladding layer 33, so as to affect the fatigue strength and the mechanical properties of the printed part. Meanwhile, the heating device in the high-vacuum environment can provide a 4D printing temperature rising environment for the laser cladding 4D printing.

[0072] The above examples are only illustrative of the present application and do not constitute a limitation on the protection scope of the present application. Any design identical or similar to the present application falls within the protection scope of the present application.

Claims

1. A laser cladding 3D / 4D printing method, characterized in that: The steps include: S1. Build a 3D model of the part to be printed based on its parameters, slice the 3D model, and generate a 2D interface diagram for each printed layer. S2, using the first laser to melt the additive manufacturing material of the current layer and form a cladding layer; S3. Use the second laser to micro-shape the surface of the cladding layer. First, adjust the process parameters of the second laser to micro-shape the surface roughness and hole defect areas of the cladding layer. Then, adjust the emission power of the second laser to irradiate the surface of the cladding layer with a point heat source to eliminate the residual stress of the cladding layer. The process parameters of the second laser for micro-shaping the surface roughness and hole defect areas of the cladding layer are adjusted according to the optical information of the cladding layer captured by the holographic camera and the surface roughness and hole defect information of the cladding layer obtained in real time by the stress wave emitted by the pulse generator. The process is as follows: use the holographic camera to obtain the cladding layer. The dynamic hologram of the cladding layer surface is analyzed by a spectrometer, and the arithmetic average roughness parameter of the cladding layer surface is calculated. Combined with the stress wave fluctuation signal obtained by the stress wave sensor, a roughness joint evaluation model of dual-modal detection is established to calculate the comprehensive roughness value of the cladding layer surface. Through the correlation mechanism of detection data and parameter adjustment, as well as the real-time feedback and closed-loop control process, the surface roughness, hole requirements and corresponding mechanical properties of the cladding layer are judged to adjust the process parameters of the second laser in real time, completing real-time laser processing correction and ultrafast laser micro-shaping of the defective area on the cladding layer surface; S4. Repeat steps S2-S3 to complete the additive manufacturing process for each layer until a printed part is obtained.

2. The laser cladding 3D / 4D printing method according to claim 1, wherein: In step S3, the emission power of the second laser for point heat source irradiation on the surface of the cladding layer is adjusted according to the residual stress information on the surface of the cladding layer obtained in real time by the X-ray stress detection device.

3. The laser cladding 3D / 4D printing method according to claim 2, wherein: The X-ray stress detection device includes an X-ray generator, an X-ray detector and an X-ray measurement recorder. The X-ray generator emits X-rays to the surface of the cladding layer, the X-ray detector detects changes in the position of X-ray diffraction peaks in the surface area of ​​the cladding layer, and the X-ray measurement recorder measures and records the diffraction angle in real time. The real-time diffraction angle data is converted and processed by an industrial computer to obtain residual stress information on the surface of the cladding layer.

4. The laser cladding 3D / 4D printing method according to claim 1, wherein: Steps S2, S3, and S4 are all performed in a vacuum heating chamber, and the pressure and temperature inside the vacuum heating chamber are controlled in real time by a vacuum pumping device and a heating device.

5. A laser cladding 3D / 4D printing system, characterized by: Used in the laser cladding 3D / 4D printing method according to any one of claims 1 to 4, comprising an industrial computer, a laser 3D / 4D printing mechanism, an ultrafast laser shaping mechanism, a holographic camera, a pulse generator, a stress wave sensor, a spectrometer, an X-ray stress detection device, and a processing platform for carrying printed parts; The laser 3D / 4D printing mechanism emits a first laser to melt the additive manufacturing material to form a cladding layer; the ultrafast laser shaping mechanism emits a second laser to shape the cladding layer; the holographic camera is electrically connected to the spectrometer, and the laser 3D / 4D printing mechanism, ultrafast laser shaping mechanism, pulse generator, stress wave sensor, spectrometer, and X-ray stress detection device are all electrically connected to the industrial control computer.

6. The laser cladding 3D / 4D printing system according to claim 5, characterized in that: The ultrafast laser shaping mechanism includes an ultrafast laser, and a first reflector, a half-wave plate, a polarization beam splitter, a spatial light modulator, a 4F optical information processing component, a second reflector and a laser probe arranged in sequence along the laser emission optical path of the ultrafast laser.

7. The laser cladding 3D / 4D printing system according to claim 6, wherein: A flip mirror is provided on the optical path between the 4F optical information processing component and the second reflector, so that a branch optical path is generated on the optical path that can be incident into the spectrometer.

8. The laser cladding 3D / 4D printing system according to claim 5, wherein: It also includes a vacuum heating chamber, in which the laser processing head of the laser 3D / 4D printing mechanism, the laser probe of the ultrafast laser shaping mechanism, the holographic camera, the pulse generator, the stress wave sensor, the X-ray stress detection device and the processing platform are all vacuum-sealed and arranged.

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