A method for improving the quality of laser powder bed fusion forming

Abstract

The present invention provides a method for improving the density of laser powder bed melting, comprising the following steps: performing three-dimensional modeling and slicing processing on a component to be processed; spreading powder on a forming substrate, and after each layer of powder is spread, performing surface rolling compaction through a rolling head to obtain a to-be-melted powder layer with a high degree of compaction; after rolling is completed, turning on a laser and performing laser powder bed melting forming on the compacted powder layer according to set process parameters; circulating surface rolling compaction and laser powder bed melting forming to realize the alternation of surface rolling and laser powder bed melting; and performing surface rolling finishing on the formed component. The present invention utilizes surface rolling to assist laser powder bed melting, expands the forming process parameter window, refines the grain size of the microstructure, inhibits the formation of metallurgical defects such as cracks and pores, greatly improves the density of the formed component, and enables the printed component to have excellent forming quality by increasing the powder layer density and introducing residual compressive stress.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and particularly relates to a method for improving the forming quality of laser powder bed melting. Background Art

[0002] After more than twenty years of development, metal additive manufacturing has become one of the fastest-growing and most promising technologies in the field of advanced manufacturing. It not only overcomes many inherent limitations in traditional production, but also significantly shortens the design and manufacturing time and reduces material waste in production. However, it has disadvantages such as high cost, long potential processing time, and expensive powder raw materials. Laser powder bed melting technology uses computer software to control a high-energy laser beam to selectively melt the metal powder in the powder bed in a protective atmosphere according to a pre-set path, realizing layer-by-layer printing and stacking forming. Since the laser moves very fast, the melted metal solidifies rapidly, inhibiting grain growth and the precipitation of alloying elements. Coupled with the disturbance effect of Marangoni flow in the molten pool, the microstructure of the material is greatly refined, so the strength and toughness of the material also increase accordingly. However, the rapid thermal cycle will generate sharp thermal gradients and possible metastable physical and chemical states, resulting in poor metallurgical defects, which is the key problem for the widespread application of all current metal additive manufacturing. Therefore, it is necessary to innovate the forming process of laser powder bed melting technology to achieve excellent forming quality by regulating the metallurgical defects and residual stress in the molten pool.

[0003] Surface rolling is a process of applying a certain pressure to the surface of a part with a hard and smooth roller, roller or ball and rolling. After surface rolling, the surface of the part is smooth and hard, and residual compressive stress is generated on the surface layer of the part. The residual compressive stress can effectively inhibit the generation and propagation of microcracks on the surface layer of the part and improve the fatigue resistance of the part. In addition, according to the metal deformation theory, when the force exerted by the rolling tool on the metal surface reaches a certain value, elastic-plastic deformation occurs on the surface of the part, dislocation and slip occur between grains, and its organizational structure and physical properties change, thus achieving the effects of surface finishing and surface strengthening.

[0004] Therefore, based on the idea of using surface rolling to generate plastic deformation to increase the powder layer density and introduce residual compressive stress, we propose a method for improving the forming quality of laser powder bed melting. This method can break through the bottleneck problems of internal stress and metallurgical defects faced by metal material additive manufacturing, realize high-performance additive manufacturing of metal components, and is of great significance for improving the level of metal material additive manufacturing in China, showing broad engineering application prospects.

[0005] The prior art discloses a method and system for regulating the deposited structure of laser additive manufacturing by ultrasonic rolling. In this invention, the additive manufacturing process parameters are set according to the workpiece and a printing program is compiled. The alloy powder fed onto the substrate surface is printed layer by layer according to the printing program until the printing of the entire workpiece is completed. Among them, during the printing process of each layer, ultrasonic rolling treatment is performed on the formed cladding layer. However, this method utilizes the improvement effect of the force effect of ultrasonic rolling on the cladding layer and does not fundamentally solve the problem of poor laser cladding forming quality, and its applicability is limited.

[0006] The prior art discloses a method for ultrasonic rolling texturing of an AlCrN coating on a substrate surface and its preparation process. In this invention, ultrasonic rolling texturing is first performed on the surface of the substrate metal, and then an AlCrN coating is prepared on the textured substrate metal surface. The process of ultrasonic rolling texturing is as follows: during the continuous ultrasonic rolling process, the substrate metal moves a set distance in the -X direction, then moves a set distance in the +Y direction, and then moves a set distance in the +X direction to form an S-shaped tool path, and the single S-shaped tool path is repeated at least 1 time to texture the surface of the substrate metal. However, this process can only enhance the mechanical properties of the substrate surface, ignores the overall mechanical properties of the material, and the action mode of the coating preparation after texturing is completely different from that of the powder layer melting.

[0007] The prior art discloses a method for laser selective melting forming gradient materials with interlayer laser modification. This invention integrates the laser surface modification process and the laser selective melting process. By means of laser beam re-scanning the formed part after a certain number of layers are formed by laser selective melting, the microstructure and properties of different regions of the part are changed, so as to obtain high-performance parts with different performance gradients. At the same time, through the re-scanning of the laser beam, defects such as voids, microcracks, and surface protrusions in the layer can be eliminated, and the density and surface quality of the formed part can be improved. The change of the microstructure and properties of the part can be achieved by adjusting the set number of layers, laser re-scanning power, laser beam scanning speed, and laser beam scanning spacing. However, this method is limited by the laser processing technology, and the strengthening effect on the interlayer is very limited, and it cannot fundamentally solve the adverse effects caused by the laser thermal effect. Summary of the Invention

[0008] Aiming at the deficiencies in the prior art, the present invention provides a method for improving the forming quality of laser powder bed melting, which can inhibit the formation of metallurgical defects during printing, improve the mechanical properties of the interior and surface of the part, and increase the practicality of the laser powder bed melting process.

[0009] The present invention achieves the above technical objectives through the following technical means.

[0010] A method for improving the forming quality of laser powder bed melting includes the following steps:

[0011] Pretreatment: Conduct three-dimensional modeling and slicing on the workpiece to be processed, set the process parameters of surface rolling and laser powder bed melting, preset the printing powder and printing environment;

[0012] Surface rolling compaction for each layer: Spread powder on the forming substrate, with the loose density greater than 55%. After each layer of powder is laid, conduct surface rolling compaction through a rolling head to obtain a powder layer to be melted with a higher degree of compaction, making its density greater than 90%;

[0013] Laser powder bed melting forming: After rolling, turn on the laser and perform laser powder bed melting forming on the compacted powder layer according to the set process parameters to obtain a solid layer with a density of 99%;

[0014] Circulation: Circulate surface rolling compaction and laser powder bed melting forming to realize the alternation of surface rolling and laser powder bed melting until the melting of the last layer of powder is completed;

[0015] Surface rolling finishing: Conduct surface rolling finishing on the formed component to reduce its surface roughness and improve the mechanical properties of the surface layer.

[0016] Furthermore, it also includes the following steps:

[0017] During the laser powder bed melting forming process of each layer, use an infrared thermal imager to monitor and feedback the temperature change of the melted powder;

[0018] Determine the area where the real-time temperature in the current layer exceeds the set threshold T1 but does not exceed T2 as the area to be hydrostatically processed. After the processing of the current layer is completed, conduct hydrostatic rolling on the area to be hydrostatically processed, and adjust the hydrostatic pressure F of rolling according to the real-time temperature to eliminate interlayer tissue and stress defects;

[0019] Determine the area where the real-time temperature in the current layer exceeds the set threshold T2 as the area to be ultrasonic vibration processed. After the processing of the current layer is completed, conduct ultrasonic vibration rolling on the area to be ultrasonic vibration processed, and adjust the ultrasonic amplitude A according to the real-time temperature to prevent deformation and cracking.

[0020] Furthermore, when the real-time temperature T detected by the sensor exceeds the set threshold T1 but does not exceed T2, the hydrostatic pressure F = F0 + k1(T - T1), and adjust the hydrostatic pressure F of rolling according to the real-time temperature T; where F0 is the initial hydrostatic pressure, k1 is the first proportionality coefficient, and the unit of k1 is N / ℃.

[0021] Furthermore, when the real-time temperature T detected by the sensor exceeds the set threshold T2, the ultrasonic amplitude A = A0 + k2(T - T2), and adjust the ultrasonic amplitude A according to the real-time temperature T, where A0 is the initial amplitude, k2 is the second proportionality coefficient, and the unit of k2 is μm / ℃.

[0022] Furthermore, the rolling head is a roller, with a rolling pressure of 200 - 5000 N, a linear velocity of 0 - 500 mm / s, and a feed rate of 1 - 100 μm.

[0023] Furthermore, the static pressure F is less than the rolling pressure for rolling and compacting each layer of powder surface; the rolling pressure used for surface rolling and finishing is greater than the rolling pressure for rolling and compacting each layer of powder surface, which can reduce the surface roughness to Ra 0.5 μm, enabling the formed component to have high surface accuracy and mechanical stability.

[0024] Furthermore, the process parameters of the laser powder bed melting are as follows: laser energy 0 - 1000 W, scanning speed 0 - 10000 mm / s, layer thickness 20 - 120 μm, and scanning spacing 70 - 200 μm.

[0025] Furthermore, the first proportionality coefficient k1 or the second proportionality coefficient k2 is respectively determined by the heating rate and is positively correlated with the heating rate.

[0026] Furthermore, after surface rolling each layer, the thickness of the powder layer is less than the original powder spreading thickness, enabling small powder particles to fill the gaps between large powder particles. The powder particles are tightly compacted, resulting in a density higher than the loose powder density, which is used to obtain residual compressive stress. The compacted powder layer is conducive to heat conduction during melting, reduces the minimum sintering energy required for forming, refines the grain structure, expands the forming process parameter window, and the introduced large residual compressive stress can also effectively inhibit the formation of metallurgical defects such as cracks and pores. Combining with the interactive additive manufacturing process greatly improves the overall quality of the formed component.

[0027] The beneficial effects of the present invention are as follows:

[0028] 1. The method for improving the quality of laser powder bed melting forming according to the present invention can significantly increase the powder layer density by "layer - by - layer" surface rolling of the powder bed, which is conducive to heat conduction during melting, expands the forming process window, and effectively refines the grain structure.

[0029] 2. The method for improving the quality of laser powder bed melting forming according to the present invention effectively inhibits the formation of metallurgical defects such as cracks and pores by increasing the powder layer density and introducing residual compressive stress, reduces the internal stress during the additive manufacturing process, and greatly improves the overall quality of the formed component.

[0030] 3. The method for improving the quality of laser powder bed melting forming according to the present invention can obtain a high - precision surface through surface rolling and finishing treatment, refine the surface layer grains, introduce residual compressive stress, improve the mechanical properties and mechanical stability of the component surface, and avoid cumbersome post - treatment means.

[0031] 4. The method for improving the quality of laser powder bed fusion forming according to the present invention has an overall fully automated operation process, reducing waste of human resources, improving work efficiency, ensuring the safety of users, enhancing the overall mechanical properties of the additive manufactured components, and having relatively high overall economy, safety, work efficiency, accuracy, and practicability.

[0032] 5. The method for improving the quality of laser powder bed fusion forming according to the present invention addresses problems such as evaporation and metallurgical defects faced during the alloy powder bed fusion forming process. According to different changes in surface temperature, hierarchical regulation is adopted for real-time adjustment. By utilizing the deformation strengthening effect of static pressure rolling and the plastic flow effect of ultrasonic vibration rolling, interlayer metallurgical defects are eliminated, induced residual compressive stress is generated, and interface bonding strength is improved, effectively controlling the forming quality between layers and achieving high-performance additive manufacturing.

[0033] 6. The method for improving the quality of laser powder bed fusion forming according to the present invention. Ultrasonic vibration rolling can not only obtain relatively high residual compressive stress but also break the columnar crystals in the molten pool to form ultrafine equiaxed crystals, achieving the synergistic strengthening and toughening of residual compressive stress / grain refinement, and effectively improving the mechanical properties of the formed components. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the processing flow of the method for improving the quality of laser powder bed fusion forming according to the present invention, where Figure 1 -a is powder spreading, Figure 1 -b is surface rolling; Figure 1 -c is laser powder bed fusion forming; Figure 1 -d is surface rolling finishing.

[0035] Figure 2 It is a schematic diagram of the morphology of loose powder according to the present invention.

[0036] Figure 3 It is a schematic diagram of the powder morphology after surface rolling according to the present invention.

[0037] Figure 4 It is a schematic diagram of the comparison of the forming quality before and after the process according to the present invention.

[0038] Figure 5 It is a schematic diagram of the comparison of the molten pool boundary structure before and after the process according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0040] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "axial", "radial", "vertical", "horizontal", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality of" means two or more, unless otherwise specifically defined.

[0041] In the present invention, unless otherwise clearly specified and defined, the terms "mount", "connect", "couple", "fix", etc. shall be construed in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0042] As Figure 1 shown, the method for improving the quality of laser powder bed fusion forming according to the present invention includes the following steps:

[0043] Step 1: Pretreatment: Model the component to be processed and import it into the slicing software for three-dimensional model slicing to obtain an STL format file. Then, determine the surface rolling and laser powder bed fusion process parameters according to the powder characteristics, compile the surface rolling and laser powder bed fusion interactive printing program, and uniformly input it into the control system to preset the printing powder and printing environment.

[0044] Step 2: Compaction of each layer by surface rolling: Start the printing program, lay powder layer by layer on the forming substrate, with the loose packing density greater than 55%. After each layer of powder is laid, perform surface rolling compaction through a rolling head to obtain a powder layer to be melted with a higher compaction degree, so that its density is greater than 90%. The process is as Figure 1 -a and Figure 1 -b shown;

[0045] Step 3: Laser powder bed fusion forming: After rolling, turn on the laser and perform laser powder bed fusion forming on the compacted powder layer according to the set process parameters to obtain a solid layer with a density as high as 99% and a high forming quality, as Figure 1 -c shown;

[0046] Step Four: Loop: Loop through Step Two and Step Three to achieve alternating surface rolling and laser powder bed melting until the melting of the last layer of powder is completed and the component is formed, then end the loop;

[0047] Step Five: Surface rolling and finishing: After printing, perform surface rolling and finishing on the formed component to reduce its surface roughness and improve the mechanical properties of the surface layer, as shown in Figure 1 -d;

[0048] Among them, interlayer surface rolling can effectively improve the powder compaction degree, introduce deeper residual compressive stress, expand the forming process parameter window, refine the grain size of the microstructure, inhibit the formation of metallurgical defects such as cracks and pores, and greatly improve the overall quality of the formed component.

[0049] In the third step, during the laser powder bed melting forming process of each layer, use an infrared thermal imager to monitor and feedback the temperature change of the molten powder; determine the area where the real-time temperature in the current layer exceeds the set threshold T1 but does not exceed T2 as the area to be hydrostatically processed. After the current layer is processed, perform hydrostatic rolling on the area to be hydrostatically processed, and adjust the hydrostatic pressure F of rolling according to the real-time temperature, which is used to eliminate interlayer microstructure and stress defects; determine the area where the real-time temperature in the current layer exceeds the set threshold T2 as the area to be ultrasonic vibration processed. After the current layer is processed, perform ultrasonic vibration rolling on the area to be ultrasonic vibration processed, and adjust the ultrasonic amplitude A according to the real-time temperature, which is used to prevent deformation and cracking.

[0050] Determine the set threshold T1 and the set threshold T2 according to the metal powder. Generally, the set threshold T1 is the boiling point temperature of the metal element, and the set threshold T2 is the boiling point temperature of the metal element + 50 - 300 degrees. If it is a metal powder of two alloys, the set threshold T1 is the boiling point temperature of the alloy element with a lower boiling point, and the set threshold T2 is the boiling point temperature of the alloy element with a higher boiling point. For example, for aluminum-lithium alloy powder, the set threshold T1 is the boiling point temperature of lithium element 1342°C; the set threshold T2 is the boiling point temperature of aluminum element 2407°C;

[0051] When the real-time temperature T detected by the sensor exceeds the set threshold T1 but does not exceed T2, the hydrostatic pressure F = F0 + k1(T - T1), and adjust the hydrostatic pressure F of rolling according to the real-time temperature T; in the formula, F0 is the initial hydrostatic pressure 200N, and k1 is the first proportionality coefficient, taking 0.7 - 1.2N / °C.

[0052] When the real-time temperature T detected by the sensor exceeds the set threshold T2, the ultrasonic amplitude A = A0 + k2(T - T2), and adjust the ultrasonic amplitude A according to the real-time temperature T. In the formula, A0 is the initial amplitude 1 - 5μm, and k2 is the second proportionality coefficient, taking 0.003 - 0.006μm / °C.

[0053] The metal powder is a special spherical powder for laser powder bed melting, which can be aluminum alloy powder, titanium alloy powder, nickel-based alloy powder. The powder particle size is 15 - 53μm, with good fluidity, high loose packing density and tapped density. The metal powder can also be alloy powder.

[0054] The surface rolling head is a roller, with a rolling force of 1000 - 5000N, a linear velocity of 0 - 500mm / s, and a feed rate of 1 - 100μm.

[0055] After surface rolling, the thickness of the powder layer is less than the original powder spreading thickness, which promotes the filling of small powder particles into the gaps between large powder particles. The powder particles obtain tight compaction, and its density is significantly higher than the loose packing density of the powder, and a large amount of residual compressive stress is introduced.

[0056] The laser powder bed melting process parameters are: laser energy 0 - 1000W, scanning speed 0 - 10000mm / s, layer thickness 20 - 120μm, and scanning spacing 70 - 200μm.

[0057] The compacted powder layer is beneficial to heat conduction during melting, reduces the minimum sintering energy required for forming, refines the grain size of the microstructure, expands the forming process parameter window, and the introduced large amount of residual compressive stress can also effectively inhibit the formation of metallurgical defects such as cracks and pores, and greatly improves the overall quality of the formed component in combination with the interactive additive manufacturing process.

[0058] The rolling force used for surface rolling and finishing is slightly greater than that for surface rolling and compaction, which can reduce the surface roughness to Ra0.5μm, making the formed component have high surface accuracy and mechanical stability.

[0059] Example 1

[0060] Taking the 15 - 53μm AlSi10Mg powder special for laser powder bed melting as an example, the method for improving the density of laser powder bed melting described in the present invention is used for additive manufacturing and forming. The specific steps are as follows:

[0061] A three-dimensional model of the part to be processed is established, and the CAD three-dimensional model of the part to be processed is preprocessed through slicing software, including slicing, repairing, supporting, etc. A laser energy of 400W, a scanning speed of 1000mm / s, a scanning spacing of 80μm, a layer thickness of 50μm, and an island scanning strategy are adopted, and then the parameters of the surface rolling equipment are set, including a static pressure of 2000N, a linear velocity of 200mm / s, a feed rate of 20μm, and a zigzag path planning. After completion, the STL file is imported into the computer control center of the laser powder bed melting equipment.

[0062] The powder and printing environment are preset. After meeting the printing requirements, the printing program is started. The interaction of the powder cylinder, the forming cylinder, and the doctor blade is controlled by the control center to complete powder spreading. Its loose packing density is 62%, as Figure 2 shown; then the surface rolling equipment is started to compact the powder, obtaining a relatively dense powder layer to be melted, with a density of 95%, as Figure 3 shown; after compaction, the doctor blade and the surface rolling device are reset.

[0063] During the laser powder bed melting forming process of each layer, a thermal imager is used to monitor and feedback the temperature change of the melted powder; the area where the real-time temperature in the current layer exceeds the set threshold T1 but does not exceed T2 is determined as the area to be hydrostatically processed. After the current layer is processed, hydrostatic rolling is performed on the area to be hydrostatically processed, and the hydrostatic pressure F of rolling is adjusted according to the real-time temperature to eliminate interlayer tissue and stress defects; the area where the real-time temperature in the current layer exceeds the set threshold T2 is determined as the area to be ultrasonic vibration processed. After the current layer is processed, ultrasonic vibration rolling is performed on the area to be ultrasonic vibration processed, and the ultrasonic amplitude A is adjusted according to the real-time temperature to prevent deformation and cracking. The set threshold T1 is the boiling point temperature of aluminum element, 2407 °C, and the set threshold T2 is the boiling point temperature of metal element, 2600 °C.

[0064] The laser is turned on to perform laser powder bed melting forming according to the set scanning strategy and process parameters. The metal powder is sintered into a solid through the thermal effect of continuous laser, obtaining a nearly fully dense forming layer, with a density of 99.5%, as Figure 4 shown. The tensile strength of Example 1 is increased by 250% compared with the prior art, greatly improving the mechanical properties of the alloy forming component.

[0065] Such a cycle of surface rolling and laser powder bed melting is carried out alternately until the entire processing process is completed. This process can effectively refine the grain of the molten pool tissue, and its internal molten pool tissue is as Figure 5 shown. After all the solid parts are printed, surface rolling and finishing treatment are carried out to reduce the surface roughness to Ra 0.5 μm, obtaining a solid part with excellent overall performance and surface performance. This process method largely solves the problem of low density in laser powder bed melting forming, expands the process parameter window, effectively refines its internal tissue grains, and can obtain components with high density, high strength, high performance, and a flat surface.

[0066] It should be understood that although this specification is described according to each embodiment, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other implementation manners that can be understood by those skilled in the art.

[0067] The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent embodiments or changes made without departing from the technical spirit of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the quality of laser powder bed fusion forming, characterized in that The steps include: Pre-processing: 3D modeling and slicing of the components to be processed, setting the surface rolling and laser powder bed melting process parameters, and pre-setting the printing powder and printing environment; Rolling and compacting the surface of each layer: Powder is spread on the forming substrate with a loose density greater than 55%. After each layer of powder is laid, the surface is rolled and compacted by a rolling head to obtain a powder layer with a high compaction degree to be melted, making its density greater than 90%; Laser powder bed fusion: After rolling is completed, the laser is turned on to perform laser powder bed fusion forming on the compacted powder layer according to the set process parameters to obtain a solid layer with a density of 99%; During the laser powder bed fusion forming process of each layer, a thermal imager is used to monitor and provide feedback on the temperature changes of the molten powder. The area in the current layer whose real-time temperature exceeds the set threshold value T1 but does not exceed T2 is determined as the area to be processed by static pressure. After the current layer is processed, the area to be processed by static pressure rolling is performed on it. The static pressure F of the rolling is adjusted according to the real-time temperature to eliminate interlayer structure and stress defects. The area in the current layer where the real-time temperature exceeds the set threshold value T2 is determined as the area to be ultrasonically processed. After the current layer is processed, the area to be ultrasonically processed is subjected to ultrasonic rolling. The ultrasonic amplitude A is adjusted according to the real-time temperature to prevent deformation and cracking. Cycle: Circulate surface rolling compaction and laser powder bed melting to achieve alternating surface rolling and laser powder bed melting until the last layer of powder is melted; Surface rolling and finishing: Surface rolling and finishing of formed components is used to reduce their surface roughness and improve the mechanical properties of the surface.

2. The method for improving the quality of laser powder bed fusion forming according to claim 1, characterized in that When the real-time temperature T detected by the sensor exceeds the set threshold T1 but does not exceed T2, the static pressure F=F0+k1(T-T1), and the rolling static pressure F is adjusted according to the real-time temperature T; where F0 is the initial static pressure, k1 is the first proportional coefficient, and the unit of k1 is N / °C.

3. The method for improving the quality of laser powder bed fusion forming according to claim 1, wherein When the real-time temperature T detected by the sensor exceeds the set threshold T2, the ultrasonic amplitude A=A0+k2(T-T2), and the ultrasonic amplitude A is adjusted according to the real-time temperature T, where A0 is the initial amplitude, k2 is the second proportional coefficient, and the unit of k2 is μm / ℃.

4. The method for improving the quality of laser powder bed fusion forming according to claim 1, characterized in that, The rolling head is a roller with a rolling force of 200-5000N, a linear speed of 0-500mm / s, and a feed rate of 1-100μm.

5. The method for improving the quality of laser powder bed fusion forming according to claim 1, characterized in that, The static pressure F is smaller than the rolling pressure of each layer of powder surface during rolling and compaction; the rolling pressure used for surface rolling and smoothing is larger than the rolling pressure of each layer of powder surface during rolling and compaction.

6. The method for improving the quality of laser powder bed fusion forming according to claim 1, characterized in that, The laser powder bed melting process parameters are: laser energy 0-1000W, scanning speed 0-10000mm / s, layer thickness 20-120μm, and scanning spacing 70-200μm.

7. The method for improving the quality of laser powder bed fusion forming according to claim 2 or 3, characterized in that, The first proportional coefficient k1 or the second proportional coefficient k2 is determined by the heating rate and is positively correlated with the heating rate.

8. The method for improving the quality of laser powder bed fusion forming according to claim 1, characterized in that After rolling the surface of each layer, the thickness of the powder layer is smaller than the original powder thickness, so that the small powder particles are filled into the gaps between the large powder particles. The powder particles are tightly compacted, making their density higher than the loose density of the powder, which is used to obtain residual compressive stress.

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