Additive manufacturing molding method and substrate cooling apparatus

Abstract

The invention provides an additive manufacturing forming method and a substrate cooling device. The additive manufacturing forming method comprises the following steps that S1, a substrate is prepared; s2, the substrate is installed in a printing device; s3, the position of the substrate is adjusted so that the powder to be printed can be flatly laid on the focusing plane of a laser beam emitted by a laser of the printing equipment; s4, starting a laser so as to melt and solidify the printing powder of the powder bed into a current layer; s5, turning off the laser for a first preset time; s6, starting a laser so as to perform in-situ remelting on the current layer formed in the step S4; wherein the step S3, the step S4, the step S5 and the step S6 are sequentially and repeatedly implemented until printing is completed. Therefore, the additive manufacturing forming method has the advantage of being beneficial to promoting epitaxial growth of the columnar crystal grains.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and in particular to an additive manufacturing forming method and a substrate cooling device. Background Art

[0002] Columnar crystal superalloys reduce the content of transverse grain boundaries and avoid the adverse effects of transverse grain boundaries on mechanical properties under high temperature environments, becoming a key material for modern aero-engine and gas turbine blades. Common methods for producing columnar crystals include casting, directional solidification (DS) and the laser energy deposition technology (DED) that has emerged in recent years. However, the disordered orientation of cast grains and the defects at the grain boundaries are the main causes of fracture failure of high-temperature service parts. Compared with traditional cast superalloys, DS superalloys have better high-temperature strength and thermal corrosion resistance, and are widely used in the manufacture of gas turbine and aero-engine turbine blades. However, they have the disadvantages of complex forming process, high cost, and difficulty in forming complex structural parts. The use of DED technology to form columnar crystals has the characteristics of high efficiency and simple operation, but because its laser trajectory is determined by the linkage of X, Y, and Z axes, the surface roughness and dimensional tolerance of the formed component are large, making it difficult to achieve direct forming of blades with fine and complex channels. Summary of the invention

[0003] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, an embodiment of the present invention provides an additive manufacturing forming method and a substrate cooling device.

[0004] The additive manufacturing forming method according to the embodiment of the present invention comprises the following steps:

[0005] S1. preparing a substrate;

[0006] S2, installing the substrate into a printing device;

[0007] S3, adjusting the position of the substrate so that the powder to be printed can be spread flat on the focal plane of the laser beam emitted by the laser of the printing device;

[0008] S4, turning on the laser to melt and solidify the printing powder of the powder bed into the current layer;

[0009] S5, turning off the laser for a first preset time;

[0010] S6, turning on the laser to remelt the current layer formed in step S4 in situ;

[0011] Wherein, step S3, step S4, step S5 and step S6 are repeatedly implemented in sequence until printing is completed.

[0012] Therefore, the additive manufacturing forming method according to the embodiment of the present invention has the advantage of promoting the epitaxial growth of columnar grains.

[0013] In some embodiments, in step S1 , at least a portion of the substrate is cooled so that a temperature of at least a portion of the substrate is less than or equal to a second preset value.

[0014] In some embodiments, in step S1, the substrate includes a first substrate and a directional solidification substrate, a first groove is opened on the upper surface of the first substrate, the directional solidification substrate is cooled so that the temperature of the directional solidification substrate is less than or equal to the second preset value, and then the directional solidification substrate is installed in the first groove so that the upper surface of the directional solidification substrate is coplanar with the upper surface of the first substrate;

[0015] In the step S3, at an initial position, the upper surface of the directional solidification substrate is located at a focal plane of the laser beam.

[0016] In some embodiments, in step S1,

[0017] placing the directional solidification substrate in liquid nitrogen to cool for a third preset time so that the temperature of the directional solidification substrate is less than or equal to the second preset value;

[0018] The temperature of the directional solidification substrate after cooling is greater than or equal to -10°C and less than or equal to 0°C.

[0019] In some embodiments, in step S1,

[0020] Placing the directionally solidified substrate in liquid nitrogen for a cooling time greater than or equal to 15 minutes;

[0021] The temperature of the directional solidification substrate after cooling is -4°C.

[0022] In some embodiments, in step S5, the time for turning off the laser is greater than or equal to 3 seconds and less than or equal to 30 seconds.

[0023] In some embodiments, in step S5, the laser is turned off for 10 seconds.

[0024] The present invention also proposes a substrate cooling device suitable for the above-mentioned additive manufacturing forming method, comprising:

[0025] A cooling box, the cooling box comprising a box body and a box cover, the box body having a placement opening, a liquid nitrogen inlet and a nitrogen outlet, and the box cover is used to cover the placement opening;

[0026] A thermometer, wherein the thermometer is disposed in the box;

[0027] A placement rack is arranged in the box and is used to support the substrate.

[0028] In some embodiments, the inner surfaces of the box cover and the box body are both provided with a heat-insulating layer;

[0029] The placement opening is opened on the top of the box body, and the box cover is located on the top of the box body;

[0030] The liquid nitrogen inlet is arranged below the placement rack, and the nitrogen outlet is arranged at the top of the side of the box body;

[0031] The thermometer includes a first thermometer and a second thermometer, wherein the first thermometer is arranged on the inner surface of the box cover, and the second thermometer is arranged on the inner surface of the bottom of the box body through a bracket, and the second thermometer is located below the placement rack.

[0032] In some embodiments, a liquid nitrogen pressure reducing valve is provided on the liquid nitrogen inlet, and the liquid nitrogen pressure reducing valve is used to adjust the flow rate of the liquid nitrogen in the liquid nitrogen inlet so that the flow rate of the liquid nitrogen in the liquid nitrogen inlet is greater than or equal to 0.2 m / s and less than or equal to 0.5 m / s;

[0033] The nitrogen outlet is provided with a liquid nitrogen pressure valve, and the liquid nitrogen pressure valve is used to adjust the pressure in the cooling box so that the pressure in the cooling box is greater than or equal to 0.5 MPa and less than or equal to 0.8 MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic diagram of a printing device according to an embodiment of the present invention.

[0035] Figure 2 is a schematic diagram of a substrate according to an embodiment of the present invention.

[0036] Figure 3 is a schematic diagram of a substrate cooling device according to an embodiment of the present invention.

[0037] Figure 4 is a schematic diagram of a substrate cooling device according to an embodiment of the present invention.

[0038] Figure 5 This is a light microscopic image of the forming area of ​​a specimen.

[0039] Figure 6 It is the grain orientation diagram of the repaired area.

[0040] Figure 7 It is an ultra-fine columnar crystal formed by laser powder bed fusion <001> Texture.

[0041] Figure numerals: 1. laser; 2. laser beam; 3. forming chamber; 4. scraper; 5. substrate; 51. first substrate; 52. directional solidification substrate; 6. waste powder barrel; 7. waste powder; 8. forming cylinder; 9. powder cylinder; 10. printing powder; 11. box body; 111. placement port; 112. liquid nitrogen inlet; 113. nitrogen outlet; 12. box cover; 13. placement rack; 14. first thermometer; 15. second thermometer; 16. liquid nitrogen pressure reducing valve; 17. liquid nitrogen pressure valve. DETAILED DESCRIPTION

[0042] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0043] The following describes the additive manufacturing forming method of the embodiment of the present invention with reference to the accompanying drawings. The present invention uses laser powder bed melting technology to achieve direct rapid forming of columnar crystal materials. Figures 1 to 7 As shown, the additive manufacturing forming method according to an embodiment of the present invention comprises the following steps:

[0044] S1. Prepare a substrate 5.

[0045] S2. Install the substrate 5 into the printing device.

[0046] S3. Adjust the position of the substrate 5 so that the powder 10 to be printed can be spread on the focal plane of the laser beam 2 emitted by the laser 1 of the printing device. Specifically, the printing powder 10 can be spread on the focal plane of the laser beam 2 emitted by the laser 1 of the printing device and form a powder bed.

[0047] S4, turn on the laser 1 to melt and solidify the printing powder 10 of the powder bed into the current layer. Specifically, the printing powder 10 is melted and solidified for the first time to form the first stage of the current layer.

[0048] S5, turning off the laser 1 for a first preset time, thereby allowing the current layer that has just been melted to cool.

[0049] S6, turning on the laser 1 to remelt the current layer (at the focal plane of the laser beam 2) formed in step S4 in situ. Specifically, after the current layer is cooled, the laser 1 is turned on again so that the laser beam 2 can melt the current layer formed in step S4 again, and the laser 1 is turned off after a certain period of time to complete the second stage of the current layer, thereby completing the printing of the current layer.

[0050] The steps S3, S4, S5 and S6 are repeated in sequence until the printing is completed. Specifically, the steps S3, S4, S5 and S6 are repeated in sequence for multiple times to complete the multi-layer printing.

[0051] According to the additive manufacturing forming method of the embodiment of the present invention, when printing the current layer (formed by melting the printing powder 10), the printing powder 10 is first melted to form the current layer (first stage), and then the current layer (first stage) is cooled, and then the current layer (first stage) is remelted in situ to form the current layer of the finished product. In this way, the temperature gradient between adjacent layers can be increased, and the growth of columnar grains can be promoted. In addition, the surface roughness and dimensional tolerance of the formed component are small, so as to realize the direct forming of blades with fine and complex channels.

[0052] Therefore, the additive manufacturing forming method according to the embodiment of the present invention has the advantage of promoting the epitaxial growth of columnar grains.

[0053] The following is a detailed description of the additive manufacturing method according to an embodiment of the present invention in conjunction with a printing device. Specifically, a sample model is first established, and three-dimensional modeling is performed during the laser powder bed fusion forming process. First, a three-dimensional model of the part is drawn, and the drawn three-dimensional model is sliced ​​layer by layer using software, and the cross-sectional information is saved on the two-dimensional slices to generate file data.

[0054] Step S1, preparing a substrate 5.

[0055] In step S1, at least a portion of the substrate 5 is cooled so that the temperature of at least a portion of the substrate 5 is less than or equal to a second preset value. The purpose of cooling the substrate 5 is to increase the temperature gradient during laser powder bed melting and promote epitaxial growth of columnar grains.

[0056] like Figure 2 As shown, in step S1, the substrate 5 includes a first substrate 51 and a directional solidification substrate 52. Specifically, the directional solidification substrate 52 is made of the same material as the printing powder 10. During the laser powder bed melting process, the crystal structure of the substrate 5 has an influence on the crystal growth orientation of the formed part, and the columnar crystal substrate of the directional solidification substrate 52 (DS substrate) is more conducive to the epitaxial growth of columnar grains during the forming process.

[0057] A first groove is formed on the upper surface of the first substrate 51, and after the directional solidification substrate 52 is cooled so that the temperature of the directional solidification substrate 52 is less than or equal to the second preset value, the directional solidification substrate 52 is installed in the first groove so that the upper surface of the directional solidification substrate 52 is coplanar with the upper surface of the first substrate 51. For example, a first groove of 100 mm × 100 mm × 20 mm is cut on a stainless steel substrate of 245 mm × 245 mm × 30 mm by machining, and a directional solidification substrate 52 of 100 mm × 100 mm × 20 mm is made so that the directional solidification substrate 52 is placed in the first groove. The first electrode 51 is a 304L stainless steel substrate, and the directional solidification substrate 52 and the printing powder 10 are made of a nickel-based super alloy (CM247LC).

[0058] In step S1, the directional solidification substrate 52 is placed in liquid nitrogen for cooling for a third preset time so that the temperature of the directional solidification substrate 52 is less than or equal to the second preset value. Specifically, the temperature of the directional solidification substrate 52 after cooling is greater than or equal to -10°C and less than or equal to 0°C. The directional solidification substrate 52 is placed in liquid nitrogen for a cooling time greater than or equal to 15 minutes. For example, the directional solidification substrate 52 is placed in liquid nitrogen for rapid cooling, and is taken out after being kept warm for 30 minutes, and the directional solidification substrate 52 is placed in the first tank.

[0059] In some embodiments, the temperature of the directionally solidified substrate 52 after cooling is -4°C.

[0060] Step S2, installing the substrate 5 into the printing device. Specifically, the substrate 5 is installed on the adjustment device of the printing cylinder 8, the thickness direction of the substrate 5 is the up-down direction, and the exposed surface of the directional solidification substrate 52 faces the upper side. Clean the forming chamber 3, and introduce inert gas (argon) to prepare for gas washing, so as to clean the forming chamber 3.

[0061] Step S3, adjust the position of the substrate 5 so that the powder 10 to be printed can be spread flat on the focal plane of the laser beam 2 emitted by the laser 1 of the printing device. Specifically, during the printing process, the substrate 5 is lowered, the powder cylinder 9 is raised, the printing powder 10 is loaded, and the laser 1 prints according to the set scanning path. For example, the substrate 5 is lowered so that the plane of the substrate 5 is located at the focal plane of the laser beam 2; the forming cylinder 8 is filled with the printing powder 10.

[0062] In some embodiments, in step S3, at the initial position, the upper surface of the directional solidification substrate 52 is located at the focal plane of the laser beam 2, so as to facilitate the printing powder 10 to be spread on the directional solidification substrate 52 to form a powder bed.

[0063] Step S4, turn on the laser 1 to melt and solidify the printing powder 10 of the powder bed into the current layer. Specifically, the equipment forming control software reads the file, and the scraper 4 spreads a layer of printing powder 10 on the substrate 5, and can scrape the printing powder 10 (metal powder) on the powder cylinder 9 onto the substrate 5, and flatten the forming cylinder 8 so that the two are on the same horizontal plane. The waste powder 7 can be scraped into the waste powder barrel 6, and the laser 1 is turned on under the control of the computer, and the printing powder 10 (metal powder) in the slicing area is melted by the laser beam, and the optimized columnar crystal forming process parameters are used for forming to form the current layer (the first stage).

[0064] Step S5, turn off the laser 1 for a first preset time. After the current layer (of the first stage) is formed, the position of the substrate 5 remains unchanged, the laser 1 is turned off, and a pause is performed between layers. In this way, the current layer (of the first stage) that has just been melted and formed can be cooled.

[0065] In step S5, the time for turning off the laser 1 is greater than or equal to 3 seconds and less than or equal to 30 seconds. For example, in step S5, the time for turning off the laser 1 is 10 seconds.

[0066] Step S6, turn on the laser 1 to remelt the current layer (at the focal plane of the laser beam 2) formed in step S4 in situ. Specifically, after the current layer (of the first stage) cools down, turn on the laser 1 again and perform in-situ remelting using the original scanning parameters to increase the temperature gradient between adjacent layers (the current layer and the previous printed layer) and promote the growth of columnar grains, so that the current layer (second stage) can be formed. Turn off the laser 1 after completing the in-situ remelting of the current layer.

[0067] Steps S3, S4, S5 and S6 are repeated in sequence until the printing is completed. After the in-situ remelting is formed into the current layer, the substrate 5 is lowered by a layer thickness, the powder cylinder 9 is raised by 1.5-2 layer thicknesses (printing slices), and the scraper 4 is re-laid with a layer of printing powder 10 (metal powder). The above process is repeated, layer by layer, until the metal part is printed. After printing, the powder is cleaned, machined, and other processes are performed.

[0068] After printing is completed, the sample can be subjected to metallographic processing, the sample can be observed and the structure can be analyzed. For example, in a specific embodiment of laser powder bed fusion forming CM247LC ultrafine columnar crystals, metallographic processing is performed after printing is completed, the sample can be observed and the structure can be analyzed. Figure 5 The light microscope image of the forming area is as follows: Figure 6 It is the organization orientation diagram (the grain orientation diagram of the repaired area organization), that is, the organization grain orientation diagram. Figure 5 and Figure 6 As shown, it has been realized <001> Oriented (preferred orientation of high-temperature alloys) columnar grains grow epitaxially along the substrate. Figure 7Laser powder bed fusion forming CM247LC ultra-fine columnar crystal <001> Texture. After observing the sample structure, it can be found that the ultra-fine columnar crystal structure formed by laser powder bed melting is within the range of 4mm*3mm. <001> The texture content can reach more than 90%, which can realize the preparation of ultrafine columnar crystals.

[0069] The present invention uses laser powder bed melting technology to form ultrafine columnar crystal materials. The forming substrate of the directional solidification substrate 52 is cooled by liquid nitrogen to increase the temperature gradient during the forming process. In the forming process, a strategy of in-situ remelting after pausing between layers (for a period of time) is adopted to achieve active regulation of the epitaxial growth of columnar crystals, control the epitaxial growth of columnar crystals, prepare ultrafine columnar crystals, and achieve rapid forming of columnar crystal components. In addition, compared with directional solidification and direct laser energy deposition technologies, laser powder bed melting technology has the characteristics of high precision and denser formed components, and can realize direct forming and repair of blades with complex cooling structures, such as complex structure blades with fine cooling channels. Laser powder bed melting forming of CM247LC high-temperature alloy can achieve a full columnar crystal structure, <001> The texture ratio is greater than 90%. The specific parameters are: laser power 150W-200W, scanning rate 750mm / s-1000mm / s, scanning spacing 40μm-80μm, powder layer thickness 30μm-40μm.

[0070] like Figure 3 and Figure 4 As shown, the present invention further proposes a substrate cooling device suitable for the additive manufacturing forming method according to an embodiment of the present invention. The substrate cooling device according to the embodiment of the present invention includes a cooling box, a thermometer and a placement rack 13.

[0071] The cooling box includes a box body 11 and a box cover 12. The box body 11 has a placement port 111, a liquid nitrogen inlet 112 and a nitrogen outlet 113. The box cover 12 is used to cover the placement port 111. Specifically, the inner surfaces of the box cover 12 and the box body 11 are provided with a heat preservation layer. The placement port 111 is opened at the top of the box body 11, and the box cover 12 is located at the top of the box body 11. The liquid nitrogen inlet 112 is arranged below the placement rack 13, and the nitrogen outlet 113 is arranged at the top of the side of the box body 11. For example, the box body 11 and the box cover 12 are made of stainless steel. The liquid nitrogen inlet 112 and the nitrogen outlet 113 are located on both sides of the box body 11 facing away.

[0072] The thermometer is arranged in the box 11. Specifically, the thermometer includes a first thermometer 14 and a second thermometer 15, the first thermometer 14 is arranged on the inner surface of the box cover 12, and the second thermometer 15 is arranged on the inner surface of the bottom of the box 11 through a bracket, and the second thermometer 15 is located below the placement rack 13.

[0073] The placement rack 13 is arranged in the box body 11, and the placement rack 13 is used to support the substrate 5. For example, the placement rack 13 is made of a plurality of metal bars arranged side by side.

[0074] The substrate cooling device according to the embodiment of the present invention facilitates cooling of the substrate 5 (directional solidification substrate 52 ).

[0075] In some embodiments, a liquid nitrogen pressure reducing valve 16 is provided on the liquid nitrogen inlet 112, and the liquid nitrogen pressure reducing valve 16 is used to adjust the flow rate of the liquid nitrogen in the liquid nitrogen inlet 112 so that the flow rate of the liquid nitrogen in the liquid nitrogen inlet 112 is greater than or equal to 0.2 m / s and less than or equal to 0.5 m / s. A liquid nitrogen pressure valve 17 is provided on the nitrogen outlet 113, and the liquid nitrogen pressure valve 17 is used to adjust the pressure in the cooling box so that the pressure in the cooling box is greater than or equal to 0.5 MPa and less than or equal to 0.8 MPa.

[0076] The substrate cooling device according to the embodiment of the present invention comprises the following steps when cooling the substrate 5 (directional solidification substrate 52):

[0077] a. After the worker wears a liquid nitrogen protective mask and gloves, he opens the box cover 12, places the directional solidification substrate 52 of the substrate 5 on the placement rack 13 in the box body 11, and covers the box cover 12.

[0078] b. Open the liquid nitrogen pressure valve 17, adjust the pressure and flow rate, and wait for the liquid nitrogen to contact the directionally solidified substrate 52 and volatilize into nitrogen gas and flow out from the nitrogen outlet 113. For example, the liquid nitrogen pressure valve 17 is used to adjust the pressure in the cooling box so that the pressure in the cooling box is greater than or equal to 0.5 MPa and less than or equal to 0.8 MPa.

[0079] c. Fill the liquid nitrogen from the liquid nitrogen inlet 112, adjust the liquid nitrogen pressure reducing valve 16, control the flow rate of the liquid nitrogen entering, and perform heat preservation cooling. For example, the liquid nitrogen pressure reducing valve 16 is used to adjust the flow rate of the liquid nitrogen in the liquid nitrogen inlet 112 so that the flow rate of the liquid nitrogen in the liquid nitrogen inlet 112 is greater than or equal to 0.2 m / s and less than or equal to 0.5 m / s.

[0080] d. Read the first thermometer 14 and the second thermometer 15. When the readings of the first thermometer 14 and the second thermometer 15 are close to the target temperature, adjust the flow rate of liquid nitrogen and nitrogen gas, and control the temperature for heat preservation. In this experiment, in order to take both cracks and tissues into consideration, the temperature gradient should not be increased too much. The temperature of the directional solidification substrate 52 is -10℃-0℃. The actual temperature of the directional solidification substrate 52 can be adjusted accordingly according to the sensitivity of the cracks in the forming material.

[0081] e. After the preset cooling time, close the liquid nitrogen inlet 112. After no gas is discharged from the nitrogen outlet 113, wear protective measures and take out the directional solidification substrate 52.

[0082] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0083] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0084] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0085] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0086] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0087] Although the above embodiments have been shown and described, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those of ordinary skill in the art are all within the scope of protection of the present invention.

Claims

1. An additive manufacturing method, characterized in that: The following steps are involved: S1. preparing a substrate; S2, installing the substrate into a printing device; S3, adjusting the position of the substrate so that the powder to be printed can be spread flat on the focal plane of the laser beam emitted by the laser of the printing device; S4, turning on the laser to melt and solidify the printing powder of the powder bed into the current layer; S5, turning off the laser for a first preset time; S6, turning on the laser to remelt the current layer formed in step S4 in situ; Wherein, step S3, step S4, step S5 and step S6 are repeatedly implemented in sequence until printing is completed.

2. The additive manufacturing method according to claim 1, characterized in that: In step S1 , at least a portion of the substrate is cooled so that a temperature of at least a portion of the substrate is less than or equal to a second preset value.

3. The additive manufacturing forming method according to claim 2, characterized in that: In step S1, the substrate includes a first substrate and a directional solidification substrate, a first groove is opened on the upper surface of the first substrate, the directional solidification substrate is cooled so that the temperature of the directional solidification substrate is less than or equal to the second preset value, and then the directional solidification substrate is installed in the first groove so that the upper surface of the directional solidification substrate is coplanar with the upper surface of the first substrate; In the step S3, at an initial position, the upper surface of the directional solidification substrate is located at a focal plane of the laser beam.

4. The additive manufacturing method according to claim 3, characterized in that: In step S1, placing the directional solidification substrate in liquid nitrogen to cool for a third preset time so that the temperature of the directional solidification substrate is less than or equal to the second preset value; The temperature of the directional solidification substrate after cooling is greater than or equal to -10°C and less than or equal to 0°C.

5. The additive manufacturing method according to claim 4, characterized in that: In step S1, Placing the directionally solidified substrate in liquid nitrogen for a cooling time greater than or equal to 15 minutes; The temperature of the directional solidification substrate after cooling is -4°C.

6. The additive manufacturing method according to any one of claims 1 to 5, characterized in that: In step S5, the laser is turned off for a period of time greater than or equal to 3 seconds and less than or equal to 30 seconds.

7. The additive manufacturing method according to claim 6, characterized in that: In step S5, the laser is turned off for 10 seconds.

8. A substrate cooling device suitable for the additive manufacturing forming method according to any one of claims 2 to 5, characterized in that: include A cooling box, the cooling box comprising a box body and a box cover, the box body having a placement opening, a liquid nitrogen inlet and a nitrogen outlet, and the box cover is used to cover the placement opening; A thermometer, wherein the thermometer is disposed in the box; A placement rack is arranged in the box and is used to support the substrate.

9. The substrate cooling device according to claim 8, characterized in that: The inner surfaces of the box cover and the box body are both provided with a heat-insulating layer; The placement opening is opened on the top of the box body, and the box cover is located on the top of the box body; The liquid nitrogen inlet is arranged below the placement rack, and the nitrogen outlet is arranged at the top of the side of the box body; The thermometer includes a first thermometer and a second thermometer, wherein the first thermometer is arranged on the inner surface of the box cover, and the second thermometer is arranged on the inner surface of the bottom of the box body through a bracket, and the second thermometer is located below the placement rack.

10. The substrate cooling device according to claim 9, characterized in that: A liquid nitrogen pressure reducing valve is provided on the liquid nitrogen inlet, and the liquid nitrogen pressure reducing valve is used to adjust the flow rate of the liquid nitrogen in the liquid nitrogen inlet so that the flow rate of the liquid nitrogen in the liquid nitrogen inlet is greater than or equal to 0.2 m / s and less than or equal to 0.5 m / s; The nitrogen outlet is provided with a liquid nitrogen pressure valve, and the liquid nitrogen pressure valve is used to adjust the pressure in the cooling box so that the pressure in the cooling box is greater than or equal to 0.5 MPa and less than or equal to 0.8 MPa.

Images