A method for manufacturing a superconducting magnet coil case of a stellarator based on an additive manufacturing technology

Abstract

The application provides a manufacturing method of a superconducting magnet coil box of a stellarator based on an additive manufacturing technology, the coil box comprises a main body part, a cooling channel peripheral wall and a transition part between the main body part and the cooling channel peripheral wall, and the manufacturing method comprises the following steps: preparing a first additive powder and a second additive powder, the first additive powder comprises stainless steel, and the second additive powder comprises copper; layer-by-layer deposition of the first additive powder is carried out by using first process parameters to form the main body part; layer-by-layer deposition of mixed powder of the first additive powder and the second additive powder is carried out by using gradient process parameters to form the transition part, and layer-by-layer deposition of the second additive powder is carried out by using second process parameters to form the cooling channel peripheral wall; and the superconducting magnet coil box of the stellarator is manufactured by using the additive manufacturing technology, so that the mechanical strength of the coil box is improved, and the heat exchange efficiency of the cooling medium in the cooling channel and the coil box is improved.

Description

Technical Field

[0001] This invention belongs to the field of nuclear fusion device manufacturing, and specifically relates to a method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology. Background Technology

[0002] A stellarator superconducting magnet is a magnetic confinement fusion device that uses a complex asymmetric three-dimensional magnetic field configuration to confine plasma. The stellarator superconducting magnet coil housing is the main supporting structure of the coil, bearing the enormous electromagnetic load under operating conditions. It is a crucial component of the stellarator superconducting magnet system, and its geometric accuracy and structural strength directly affect the magnetic field accuracy and even plasma performance. The stellarator superconducting magnet system must meet the following requirements: the magnet coil must strictly follow a pre-defined three-dimensional spatial curve (such as a spiral or modular polygon) to generate a magnetic field with rotational transformation, thereby avoiding plasma disruption instabilities caused by plasma currents in tokamak devices; this spatial geometric complexity makes manufacturing the coil housing using traditional two-dimensional machining and planar welding processes extremely difficult, and dimensional accuracy is hard to control; the magnetic field error of the stellarator superconducting magnet must be controlled within 10... -4 The magnitude of the geometric deviations of the coil box (such as local deformation or assembly misalignment) will directly lead to magnetic field distortion and affect the plasma confinement performance. The coil box needs to maintain structural integrity under extremely low temperatures below 4.2 K (liquid helium temperature range) and high electromagnetic loads (such as Lorentz force under magnetic fields above 10T), requiring the coil box to have good resistance to brittle fracture in low temperature environments.

[0003] The traditional stellarator superconducting magnet coil box mainly adopts the following processes: (1) Segmented machining + welding: The three-dimensional coil box body and the outer connecting and supporting structure are decomposed into multiple planar or simple curved surface segments, which are then welded together after being processed by CNC machine tools. This process has the problem that residual stress is easily generated in the weld area (especially the irregular curved surface joints), and the deformation is large when shrinking at low temperature, which exceeds the tolerance range of the stellarator magnetic field accuracy (usually <0.2mm). (2) Vacuum brazing process of cooling channel: The channel and the box body are manufactured separately and connected by brazing materials (such as Ag-Cu alloy). There is a 10-50μm brazing layer at the interface. This process has the problem that the thermal conductivity of the brazing layer drops sharply at low temperature (such as the thermal conductivity of Ag-Cu at 4K is only 1 / 10 of that at room temperature), forming a significant contact thermal resistance, thereby reducing the cooling efficiency of the coil box. There is also the problem that the brazing mechanical strength is not high, and the thermal stress may cause the cooling tube to peel off the coil box during the coil cooling process. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of large deformation due to low-temperature shrinkage caused by welds in existing stellarator superconducting magnet coil box manufacturing methods, and the unstable connection between the cooling channel and the main body of the box due to welding, which reduces the cooling efficiency of the coil box.

[0005] To address the aforementioned technical problems, embodiments of the present invention disclose a method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology. The coil box includes a main body, a cooling channel peripheral wall, and a transition portion located between the main body and the cooling channel peripheral wall. The manufacturing method includes:

[0006] S1: Prepare additive powder, which includes a first additive powder and a second additive powder. The first additive powder includes stainless steel, and the second additive powder includes copper.

[0007] S2: Determine the principal stress direction of the target coil box, and slice the coil box model based on the principal stress direction, wherein the grains are oriented to grow along the principal stress direction of the coil box, and obtain the selective laser melting process parameters; the selective laser melting process parameters include the first process parameter, the second process parameter, and the gradient process parameter.

[0008] S3: The first additive powder is deposited layer by layer using the first process parameters to form the main body; the mixed powder of the first additive powder and the second additive powder is deposited layer by layer using the gradient process parameters to form the transition part; and the second additive powder is deposited layer by layer using the second process parameters to form the cooling channel peripheral wall.

[0009] S4: Post-processing of the printed coil box, including hot isostatic pressing and cooling.

[0010] According to another specific embodiment of the present invention, a method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology is disclosed. The first process parameters include: laser power of 200-350W, scanning speed of 800-1200mm / s, layer thickness of 30-50μm, substrate preheating temperature of 300-400℃, and protective gas flow rate of 10-15L / min. The second process parameters include: laser power of 400-600W, scanning speed of 500-700mm / min, layer thickness of 50-80μm, substrate preheating temperature of 150-250℃, and protective gas flow rate of 10-15L / min.

[0011] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology, wherein the gradient process parameters include: laser power of 300-450W, scanning speed of 700-800mm / min, layer thickness of 40-60μm, substrate preheating temperature of 200-300℃, and protective gas flow rate of 10-15L / min.

[0012] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology. The mixed powder includes five gradient mixed powders, wherein the volume content of the second additive powder in the first gradient mixed powder is 5%, the volume content of the second additive powder in the second gradient mixed powder is 25%, the volume content of the second additive powder in the third gradient mixed powder is 50%, the volume content of the second additive powder in the fourth gradient mixed powder is 75%, and the volume content of the second additive powder in the fifth gradient mixed powder is 95%.

[0013] The gradient process parameters include five gradient process parameters. The first gradient process parameters include: laser power of 350W, scanning speed of 900mm / s, layer thickness of 30μm, substrate preheating temperature of 350℃, and protective gas flow rate of 15L / min. The second gradient process parameters include: laser power of 400W, scanning speed of 800mm / min, layer thickness of 30μm, substrate preheating temperature of 300℃, and protective gas flow rate of 15L / min. The third gradient process parameters include: laser power of 450W, scanning speed of 800mm / s, layer thickness of 30μm, substrate preheating temperature of 300℃, and protective gas flow rate of 15L / min. The first gradient process parameters are: 700 mm / s scanning speed, 40 μm layer thickness, 300 °C substrate preheating temperature, and 15 L / min protective gas flow rate; the second gradient process parameters are: 450 W laser power, 700 mm / min scanning speed, 50 μm layer thickness, 250 °C substrate preheating temperature, and 15 L / min protective gas flow rate; the third gradient process parameters are: 500 W laser power, 600 mm / min scanning speed, 60 μm layer thickness, 250 °C substrate preheating temperature, and 15 L / min protective gas flow rate.

[0014] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology, wherein the number of deposition layers of the first gradient mixed powder and the fifth gradient mixed powder are both 15 layers, the number of deposition layers of the second gradient mixed powder and the fourth gradient mixed powder are both 20 layers, and the number of deposition layers of the third gradient mixed powder is 25 layers.

[0015] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology. Step S2 further includes: before slicing the coil box model, dividing the coil box model into multiple sub-models along its circumference, and slicing each sub-model separately; in step S3, depositing multiple coil box segments corresponding to the multiple sub-models respectively, and splicing the printed multiple coil box segments together. According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology. The stainless steel is composed of the following chemical elements by mass percentage: C: 0.01~0.03%, Si: 0.45~0.75%, Mn: 1.65~2.00%, Cr: 16.0~18.5%, Mo: 2.00~2.50%, Ni: 11.0~14.0%, Co: 0.07~0.1%; the balance being Fe and unavoidable impurities.

[0016] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology, wherein the first additive powder further includes TiC nanoparticles, and the volume of TiC nanoparticles accounts for 1%-10% of the volume of the first additive powder.

[0017] According to another specific embodiment of the present invention, an embodiment of the present invention discloses a method for manufacturing a superconducting magnet coil box for a stellarator based on additive manufacturing technology. In step S4, the temperature is raised to 800°C and hot isostatic pressing is performed under 100MPa argon gas conditions; then the temperature is cooled for 20-24 hours at a temperature of -130 to -196°C.

[0018] The beneficial effects of this invention are:

[0019] This invention utilizes additive manufacturing technology to fabricate the superconducting magnet coil box for a stellarator. Compared to traditional welding methods, additive manufacturing reduces stress shrinkage caused by welding and extensive machining, significantly improving manufacturing precision and material utilization efficiency. It also enables the printing of cantilevered curved surfaces with little or no support. Furthermore, additive manufacturing allows the coil box body and the cooling channel perimeter to be printed integrally, placing the cooling channels within the coil box wall. This enhances the overall structural integrity and mechanical strength of the stellarator superconducting magnet coil box, while reducing the thermal resistance between the cooling medium and the coil box, thus improving heat exchange efficiency. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the cross-sectional structure of a portion of the wall of the superconducting magnet coil box of the stellarator provided by the present invention;

[0021] Figure 2 This is a schematic diagram of the structure of the stellarator superconducting magnet coil box model provided by the present invention.

[0022] Explanation of reference numerals in the attached figures:

[0023] 1. Main body; 2. Cooling channel perimeter wall; 3. Transition section. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0025] This invention provides a method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology. The stellarator superconducting magnet coil box is the main supporting structure of the superconducting coil. Based on the structure of the stellarator superconducting coil, the stellarator superconducting magnet coil box is a non-planar irregular structure with large-angle twists in some areas, resulting in a complex shape. The manufacturing method includes the following steps S1-S4, and the specific preparation steps are described in detail below.

[0026] S1: Prepare additive powder, which includes a first additive powder and a second additive powder.

[0027] It should be noted that, as Figure 1 As shown, the stellarator superconducting magnet coil box has multiple cooling channels extending along the coil box's extension direction, and these channels have coolant inlets and outlets. When the coil box is applied to the stellarator, coolant (such as liquid helium) flows through the cooling channels to eliminate heat deposition on the coil box during magnet operation and prevent heat transfer to the coil. Therefore, the coil box includes a main body 1 and cooling channel peripheral walls 2. A first additive powder is used to prepare the coil box main body, and a second additive powder is used to prepare the cooling channel peripheral walls 2. The coil box also includes a transition section 3 located between the main body 1 and the cooling channel peripheral walls 2, prepared by mixing the first and second additive powders. This creates a material transition between the cooling channel peripheral walls 2 and the coil box main body 1, improving the heat exchange efficiency between the cooling medium and the coil box.

[0028] In this invention, the first additive powder comprises stainless steel. Since the superconducting coil needs to operate in a low-temperature environment, the stainless steel material should possess good low-temperature toughness. Specifically, it can be low-temperature austenitic stainless steel powder, such as 316LN stainless steel or 316LMn stainless steel. In one specific embodiment of this invention, the stainless steel is composed of the following chemical elements by mass percentage: C: 0.01~0.03%, Si: 0.45~0.75%, Mn: 1.65~2.00%, Cr: 16.0~18.5%, Mo: 2.00~2.50%, Ni: 11.0~14.0%, Co: 0.07~0.1%; the balance being Fe and unavoidable impurities. The impurities include P and S, with specific proportions shown in Table 1.

[0029] Table 1 Chemical composition of stainless steel (wt%)

[0030] C Si Mn P S Cr Ni Mo Co 0.01~0.03 0.45~0.75 1.65~2.00 <0.03 <0.01 16.0~18.5 11.0~14.0 2.00~2.50 0.07～0.1

[0031] Of the above components, excessive carbon (C) content reduces the material's low-temperature toughness, thus the C content in stainless steel is kept low. Manganese (Mn) increases strength and refines grain size; chromium (Cr) improves hardenability and strength; nickel (Ni) improves low-temperature crack arrest performance, reducing dislocation slip resistance and mitigating low-temperature embrittlement; molybdenum (Mo) controls phase transformation and increases strength, lowering the γα phase transformation temperature of stainless steel and refining the microstructure; cobalt (Co) forms a continuous solid solution with iron, increasing the hardness and strength of the steel and improving the toughness of martensite. The stainless steel produced in this invention uses a low-carbon design, with Mo+Cr+Co added for strengthening, increasing the strength of the coil box, and the addition of Ni ensures sufficient strength while maintaining good low-temperature crack arrest performance.

[0032] Furthermore, in one specific embodiment of the present invention, the first additive powder further includes TiC nanoparticles, and the volume of the TiC nanoparticles accounts for 1%-10% of the volume of the first additive powder, preferably 5%; wherein the TiC nanoparticles refer to micron-sized or nano-sized TiC powder (i.e., particle size within 100 nm). The TiC nanoparticles can be added to the stainless steel powder by pre-mixing. The mixing method can be mechanical mixing or pre-alloying mixing. Mechanical mixing involves placing the TiC nanoparticles and the matrix metal powder in a three-dimensional powder mixer or a V-type powder mixer for several hours of low-temperature, low-speed mixing. Pre-alloying mixing involves using high-energy ball milling, plasma spheroidization, or other techniques to firmly bond or encapsulate the TiC nanoparticles on the surface or inside of the stainless steel powder particles during the powder preparation stage. The TiC nanoparticles, as a reinforcing material, can improve the strength of the prepared coil box; further, the average particle size of the first additive powder is 15 μm to 45 μm. TiC nanopowder, as a reinforcing phase, can improve the hardness and strength of austenitic stainless steel. When used to manufacture coil boxes, it has a fine-grain strengthening effect. Using the above-mentioned first additive powder, the structural strength and toughness of the prepared coil box can reach the level of forgings, which meets the structural strength requirements of superconducting coils.

[0033] The cooling channel of the coil box should have good thermal conductivity. Therefore, the second additive powder includes copper with good thermal conductivity. Specifically, it can be oxygen-free copper powder or copper alloy powder, preferably oxygen-free copper powder. Furthermore, the average particle size of the second additive powder is 40μm to 60μm.

[0034] S2: Determine the principal stress direction of the target coil box, and slice the pre-printed stellarator superconducting magnet coil box model based on the principal stress direction to divide the specific number of printing layers and obtain the Selective Laser Melting (SLM) process parameters for additive manufacturing; wherein the SLM process parameters include a first process parameter, a second process parameter, and a gradient process parameter, wherein the first process parameter is used to form the main body of the coil box by deposition of the first additive powder, the second process parameter is used to form the cooling channel peripheral wall by deposition of the second additive powder, and the gradient process parameter is used to form the transition part by deposition of the mixed powder of the first additive powder and the second additive powder, which can be designed using FGM (Functionally Gradient Materials).

[0035] Specifically, the superconducting magnet coil box model of the stellarator to be printed can be obtained based on the three-dimensional spatial coordinates of the asymmetric coil in the stellarator magnet model (such as the "Helias" configuration stellarator) obtained from the design. Based on the topology optimization algorithm, the coil box model is converted into the scanning path of additive manufacturing. The model is sliced ​​using slicing software (such as Materialise Magics or Simplify3D). These slicing data will guide the scanning path of the laser.

[0036] It should be noted that the structural model of the coil box is as follows: Figure 2 As shown, the coil has an irregular shape. During fabrication, the printing sequence is set according to its principal stress direction. The mechanical design of the coil box needs to resist radial, axial, and tangential loads caused by magnetic force. The principal stress direction is usually closely related to the radius of curvature, helix angle, and support point position of the coil, and can be determined by simulation model. The principal stress direction of the obtained coil box can extend along the axial direction or the radial direction of the coil box. If the principal stress direction is along the axial direction, the coil box can be printed along the axial direction; if the principal stress direction is along the radial direction, the coil box can be printed along the radial direction.

[0037] In one specific embodiment, due to the large size of the coil box, before slicing the coil box model, the model is divided into multiple sub-models along its circumference, specifically 2-4 sub-models. To reduce splicing points, it is preferable to divide the coil box into two sub-models, and the division point should be at a relatively gentle position where the coil box has minimal or no angular distortion. For example, in... Figure 2 The dotted lines in the diagram are used to divide the structure, ensuring ease of subsequent assembly and greater stability of the assembled mechanism. Furthermore, the division can be based on the stress distribution in different parts of the coil box. It should be noted that during molecular modeling, a 0.1~0.5mm overlap area needs to be maintained at the end face of the division point; in this invention, the preferred overlap area is 0.4mm.

[0038] In one specific embodiment, the first process parameters include: laser power of 200-350W, scanning speed of 800-1200mm / s, layer thickness of 30-50μm, substrate preheating temperature of 300-400℃, and protective gas flow rate of 10-15L / min.

[0039] Using the above process parameters, cantilever curved surface printing with no or little support can be achieved, with a forming accuracy of ±0.05mm / m, and continuous transition structures with a twist angle of up to 30° can be printed.

[0040] In one specific embodiment, the second process parameters include: laser power of 400-600W, scanning speed of 500-700mm / min, layer thickness of 50-80μm, substrate preheating temperature of 150-250℃, and protective gas flow rate of 10-15L / min.

[0041] In one specific embodiment, the gradient process parameters include: laser power of 300-450W, scanning speed of 700-800mm / min, layer thickness of 40-60μm, substrate preheating temperature of 200-300℃, and protective gas flow rate of 10-15L / min.

[0042] Furthermore, in one specific embodiment, the mixed powder of the first additive powder and the second additive powder includes n gradient mixed powders with different proportions, wherein the content of the second additive powder increases from the first gradient mixed powder to the nth gradient mixed powder, and correspondingly, the content of the first additive powder decreases accordingly; the gradient process parameters include n gradient process parameters that correspond to the n gradient mixed powders and vary accordingly, wherein the first gradient process parameter is closer to the first process parameter, and the nth gradient process parameter is closer to the second process parameter.

[0043] Furthermore, in one specific embodiment, the mixed powder includes five gradient mixed powders, wherein the volume content of the second additive powder in the first gradient mixed powder is 5%, the volume content of the second additive powder in the second gradient mixed powder is 25%, the volume content of the second additive powder in the third gradient mixed powder is 50%, the volume content of the second additive powder in the fourth gradient mixed powder is 75%, and the volume content of the second additive powder in the fifth gradient mixed powder is 95%.

[0044] The first-tier process parameters include: laser power of 350W, scanning speed of 900mm / s, layer thickness of 30μm, substrate preheating temperature of 350℃, and protective gas flow rate of 15L / min; the second-tier process parameters include: laser power of 400W, scanning speed of 800mm / min, layer thickness of 30μm, substrate preheating temperature of 300℃, and protective gas flow rate of 15L / min; the third-tier process parameters include: laser power of 450W, scanning speed of 700mm / s. The first gradient process parameters are: layer thickness 40μm, substrate preheating temperature 300℃, and protective gas flow rate 15L / min; the second gradient process parameters are: laser power 450W, scanning speed 700mm / min, layer thickness 50μm, substrate preheating temperature 250℃, and protective gas flow rate 15L / min; the third gradient process parameters are: laser power 500W, scanning speed 600mm / min, layer thickness 60μm, substrate preheating temperature 250℃, and protective gas flow rate 15L / min.

[0045] This invention dynamically adjusts the ratio of the first additive powder and the second additive powder in the mixed powder during the preparation of the transition layer, so as to achieve a gradual transition of material composition between the main body of the coil box and the peripheral wall of the cooling channel. This can effectively reduce the stress concentration problem caused by composition differences in different areas, thereby improving the fatigue life of the coil box and the fracture resistance between the main body of the coil box and the peripheral wall of the cooling channel.

[0046] Furthermore, in one specific embodiment, the first gradient mixed powder and the fifth gradient mixed powder are each printed with 15 layers, the second gradient mixed powder and the fourth gradient mixed powder are each printed with 20 layers, and the third gradient mixed powder is printed with 25 layers. That is, the thickness of the printed transition layer is approximately 4 mm.

[0047] S3: Using SLM printing equipment, printing is performed according to SLM process parameters, including: depositing the first additive powder layer by layer using the first process parameters; depositing a mixture of the first additive powder and the second additive powder layer by layer using gradient process parameters; and depositing the second additive powder layer by layer using the second process parameters.

[0048] During the printing process, the direction of heat flow and solidification kinetics of the laser molten pool can be controlled to allow the metal grains to grow directionally along the principal stress direction of the coil box. This method can optimize the anisotropic mechanical properties of the obtained coil box, increase the tensile strength along the principal stress direction by more than 20%, reduce equiaxed grain boundaries, and lower the risk of intergranular cracks at low temperatures (the probability of brittle fracture at equiaxed grain boundaries is 3-5 times higher than that of columnar grains at 4K).

[0049] Furthermore, in-situ non-destructive testing is performed in real time during the printing process. Specifically, an integrated online process monitoring (OPM) system is used to detect the porosity between printed layers in real time through X-ray diffraction (XRD) to ensure that the defect rate is <0.02%.

[0050] In one specific implementation, in step S2 above, the coil box model is divided into multiple sub-models along its circumference. In step S3, multiple coil box segments corresponding to the multiple sub-models are deposited and formed respectively, and the multiple coil box segments printed are spliced ​​and printed.

[0051] This method allows for the determination of the principal stress directions of multiple coil box segments, and printing can be performed according to the stress directions of different segments. In other words, the printing directions of different coil box segments may be different. This approach enables the printing of different coil box segments based on their stress directions, thereby further optimizing the mechanical properties of the coil box.

[0052] The splicing printing process employs SLM technology, dividing the metal powder bed into multiple laser scanning zones. Each laser head is responsible for one sub-zone, and molecular-level bonding is achieved by melting the metal powder in the splicing overlap area. The process parameters for the splicing overlap area are adjusted based on the first process parameter, the second process parameter, and the gradient process parameter. Specifically, the laser power is increased by 10%, and the scanning speed is reduced by 5% to compensate for insufficient powder melting caused by energy attenuation at the scanning boundary between the two laser heads, thus avoiding the formation of pores or microcracks. Furthermore, the scanning path in the splicing overlap area adopts staggered scanning rather than simple splicing, eliminating scanning boundary errors of the laser heads and ensuring continuous melt path.

[0053] S4: Post-processing of the printed coil box; post-processing includes hot isostatic pressing and cooling treatment. Hot isostatic pressing is used to further improve the density of the microstructure, so that its density is basically the same as that of the ingot forging.

[0054] In one specific embodiment, the temperature is raised to 800°C, and hot isostatic pressing is performed under 100 MPa argon atmosphere. Deep cryogenic treatment at -196°C is then used to stabilize the austenitic structure and reduce residual stress to <50 MPa.

[0055] This invention utilizes additive manufacturing technology to fabricate the superconducting magnet coil box for a stellarator. Compared to traditional welding methods, additive manufacturing reduces stress shrinkage caused by welding and extensive machining, significantly improving manufacturing precision and material utilization efficiency. It also enables the printing of cantilevered curved surfaces with little or no support. Furthermore, additive manufacturing allows the coil box body and the cooling channel perimeter to be printed integrally, placing the cooling channels within the coil box wall. This enhances the overall structural integrity and mechanical strength of the stellarator superconducting magnet coil box, while reducing the thermal resistance between the cooling medium and the coil box, thus improving heat exchange efficiency.

[0056] This invention also discloses a stellarator superconducting magnet coil box prepared using the above-mentioned stellarator superconducting magnet coil box manufacturing method based on additive manufacturing technology, such as... Figure 1 As shown, the stellarator superconducting magnet coil box includes: a main body 1 printed with a first additive powder including stainless steel, a cooling channel peripheral wall 2 printed with a second additive powder including copper, and a transition part 3 located between the main body 1 and the cooling channel peripheral wall 2 and printed with a mixed powder of the first and second additive powders, wherein the cooling channel peripheral wall 2 contains a cooling channel extending along the extension direction of the coil box.

[0057] The following will further illustrate the method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology according to the present invention with reference to specific embodiments.

[0058] Example 1

[0059] A method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology includes the following steps:

[0060] S1: Prepare a first additive powder and a second additive powder. The first additive powder is a mixture of stainless steel and TiC nanoparticles. The stainless steel is composed of the following chemical elements by mass percentage: C: 0.01~0.03%, Si: 0.45~0.75%, Mn: 1.65~2.00%, Cr: 16.0~18.5%, Mo: 2.00~2.50%, Ni: 11.0~14.0%, Co: 0.07~0.1%; the balance is Fe and unavoidable impurities. The TiC nanoparticles account for 5% of the volume of the first additive powder. The second additive powder is oxygen-free copper.

[0061] S2: Slice the coil box model to obtain SLM process parameters. The first process parameters include: laser power of 300W, scanning speed of 1000mm / s, layer thickness of 40μm, substrate preheating temperature of 350℃, and protective gas flow rate of 15L / min. The second process parameters include: laser power of 500W, scanning speed of 600mm / min, layer thickness of 60μm, substrate preheating temperature of 200℃, and protective gas flow rate of 15L / min. The gradient process parameters include: laser power of 400W, scanning speed of 700mm / min, layer thickness of 50μm, substrate preheating temperature of 300℃, and protective gas flow rate of 15L / min.

[0062] S3: The first additive powder is deposited layer by layer using the first process parameters to form the main body; the mixed powder of the first additive powder and the second additive powder is deposited layer by layer using the gradient process parameters to form the transition part, wherein the volume content of the second additive powder in the mixed powder is 50% and the number of deposition layers is 80; the second additive powder is deposited layer by layer using the second process parameters to form the cooling channel perimeter wall.

[0063] S4: Post-process the printed coil box, which involves heating to 800°C and performing hot isostatic pressing under 100MPa argon gas; then cooling at -130 to -196°C for 22 hours.

[0064] Example 2

[0065] A method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology includes the following steps:

[0066] S1: Prepare a first additive powder and a second additive powder. The first additive powder is a mixture of stainless steel and TiC nanoparticles. The stainless steel is composed of the following chemical elements by mass percentage: C: 0.01~0.03%, Si: 0.45~0.75%, Mn: 1.65~2.00%, Cr: 16.0~18.5%, Mo: 2.00~2.50%, Ni: 11.0~14.0%, Co: 0.07~0.1%; the balance is Fe and unavoidable impurities. The TiC nanoparticles account for 5% of the volume of the first additive powder. The second additive powder is oxygen-free copper.

[0067] S2: Slice the coil box model to obtain SLM process parameters. The first process parameters include: laser power 300W, scanning speed 1000mm / s, layer thickness 40μm, substrate preheating temperature 350℃, and protective gas flow rate 15L / min. The second process parameters include: laser power 500W, scanning speed 600mm / min, layer thickness 60μm, substrate preheating temperature 200℃, and protective gas flow rate 15L / min. The gradient process parameters include five gradient parameters. The first gradient process parameters include: laser power 350W, scanning speed 900mm / s, layer thickness 30μm, substrate preheating temperature 350℃, and protective gas flow rate 15L / min. The second gradient process parameters include: laser power 300W, scanning speed 900mm / s, layer thickness 30μm, substrate preheating temperature 350℃, and protective gas flow rate 15L / min. The first gradient process parameters are: 400W laser power, 800mm / min scanning speed, 30μm layer thickness, 300℃ substrate preheating temperature, and 15L / min protective gas flow rate; the second gradient process parameters are: 450W laser power, 700mm / s scanning speed, 40μm layer thickness, 300℃ substrate preheating temperature, and 15L / min protective gas flow rate; the third gradient process parameters are: 450W laser power, 700mm / min scanning speed, 50μm layer thickness, 250℃ substrate preheating temperature, and 15L / min protective gas flow rate; the fourth gradient process parameters are: 500W laser power, 600mm / min scanning speed, 60μm layer thickness, 250℃ substrate preheating temperature, and 15L / min protective gas flow rate.

[0068] S3: The main body is formed by depositing the first additive powder layer by layer using the first process parameters; the transition section is formed by depositing a mixture of the first and second additive powders layer by layer using gradient process parameters. The mixture includes five gradient powders, each corresponding to one of the five gradient process parameters. The volume content of the second additive powder in the first gradient mixture is 5%, in the second gradient mixture it is 25%, in the third gradient mixture it is 50%, in the fourth gradient mixture it is 75%, and in the fifth gradient mixture it is 95%. The first and fifth gradient mixtures each have 15 deposition layers, the second and fourth gradient mixtures each have 20 deposition layers, and the third gradient mixture has 25 deposition layers. The cooling channel perimeter is formed by depositing the second additive powder layer by layer using the second process parameters.

[0069] S4: Post-process the printed coil box, which involves heating to 800°C and performing hot isostatic pressing under 100MPa argon gas; then cooling at -130 to -196°C for 22 hours.

[0070] Comparative Example 1

[0071] A method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology involves welding together the body, outer connection and support structure of the coil box obtained by CNC machine tool processing, machining grooves in the coil box wall, and then embedding oxygen-free copper cooling channels into it by vacuum brazing.

[0072] The performance of the stellarator superconducting magnet coil boxes obtained in Examples 1 and 2 and Comparative Example 1 was tested, including: measuring the centerline deviation of the stellarator superconducting magnet coil boxes obtained in Examples 1-2 and Comparative Example 1 using a laser collimator, and then calculating the centerline deviation rate between the actual and theoretical values; testing the mechanical strength of the stellarator superconducting magnet coil boxes obtained in Examples 1-2 and Comparative Example 1 at 4K according to ASTM E8 standard; testing the fracture toughness of the stellarator superconducting magnet coil boxes obtained in Examples 1-2 and Comparative Example 1 at 4K according to ASTM E1820 standard; and measuring the critical heat flux using a heat pipe generator. The results are shown in Table 2.

[0073] Table 2 Performance test results of the stellarator superconducting magnet coil box obtained in Examples 1-2 and Comparative Example 1

[0074] Example 1 Example 2 Comparative Example 1 Centerline deviation 0.01% 0.008% 0.013% fracture toughness 170MPa·m¹ / ² 180MPa·m¹ / ² 90MPa·m¹ / ² Critical heat flux 14W / mm² 15W / mm² 12 W / mm²

[0075] As shown in Table 2, the coil box fabricated using additive manufacturing technology in this invention achieves a centerline deviation rate of ≤0.01% for the non-planar twisted coil box structure, significantly improving manufacturing precision compared to Comparative Example 1 (using conventional manufacturing methods). The coil box fabricated in this invention exhibits a fracture toughness (K1c) of less than or equal to 180 MPa·m¹ / ² at 4K, a significant improvement compared to Comparative Example 1, indicating that additive manufacturing significantly enhances low-temperature toughness. Furthermore, the cooling channel of the coil box fabricated in this invention demonstrates an equivalent thermal conductivity at 4K that is more than 40% higher than that of Comparative Example 1, and an increased critical heat flux of 15 W / mm², significantly improving cooling efficiency.

[0076] It should be noted that, in addition to the specific embodiments described above, those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention is presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to these embodiments. On the contrary, the purpose of describing the invention in conjunction with the embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a deep understanding of the invention, many specific details are included in the above description, and the invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0077] It should be noted that in this specification, similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0078] While the present invention has been illustrated and described with reference to certain preferred embodiments, those skilled in the art should understand that the above description is a further detailed explanation of the invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the invention to these descriptions. Various changes in form and detail can be made by those skilled in the art, including several simple deductions or substitutions, without departing from the spirit and scope of the invention.

Claims

1. A method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology, characterized in that, The coil box includes a main body, a cooling channel peripheral wall, and a transition portion located between the main body and the cooling channel peripheral wall. The manufacturing method includes: S1: Prepare a first additive powder and a second additive powder, wherein the first additive powder comprises stainless steel and the second additive powder comprises copper; S2: Determine the principal stress direction of the target coil box, and slice the coil box model based on the principal stress direction, wherein the grains are oriented to grow along the principal stress direction of the coil box, and the selected area laser melting process parameters are obtained; the selected area laser melting process parameters include a first process parameter, a second process parameter, and a gradient process parameter; S3: The first additive powder is deposited layer by layer using the first process parameters to form the main body; the mixed powder of the first additive powder and the second additive powder is deposited layer by layer using the gradient process parameters to form the transition part; the second additive powder is deposited layer by layer using the second process parameters to form the cooling channel peripheral wall. S4: Post-process the printed coil box, the post-processing including hot isostatic pressing and cooling.

2. The method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology as described in claim 1, characterized in that, The first process parameters include: laser power of 200-350W, scanning speed of 800-1200mm / s, layer thickness of 30-50μm, substrate preheating temperature of 300-400℃, and protective gas flow rate of 10-15L / min; the second process parameters include: laser power of 400-600W, scanning speed of 500-700mm / min, layer thickness of 50-80μm, substrate preheating temperature of 150-250℃, and protective gas flow rate of 10-15L / min.

3. The method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology as described in claim 2, characterized in that, The gradient process parameters include: laser power of 300-450W, scanning speed of 700-800mm / min, layer thickness of 40-60μm, substrate preheating temperature of 200-300℃, and protective gas flow rate of 10-15L / min.

4. The method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology as described in claim 3, characterized in that, The mixed powder comprises five gradient mixed powders, wherein the volume content of the second additive powder in the first gradient mixed powder is 5%, the volume content of the second additive powder in the second gradient mixed powder is 25%, the volume content of the second additive powder in the third gradient mixed powder is 50%, the volume content of the second additive powder in the fourth gradient mixed powder is 75%, and the volume content of the second additive powder in the fifth gradient mixed powder is 95%. The gradient process parameters include five gradient process parameters. The first gradient process parameters include: laser power of 350W, scanning speed of 900mm / s, layer thickness of 30μm, substrate preheating temperature of 350℃, and protective gas flow rate of 15L / min. The second gradient process parameters include: laser power of 400W, scanning speed of 800mm / min, layer thickness of 30μm, substrate preheating temperature of 300℃, and protective gas flow rate of 15L / min. The third gradient process parameters include: laser power of 450W, scanning speed of 800mm / s, layer thickness of 30μm, substrate preheating temperature of 300℃, and protective gas flow rate of 15L / min. The first gradient process parameters are: a scanning speed of 700 mm / s, a layer thickness of 40 μm, a substrate preheating temperature of 300 °C, and a protective gas flow rate of 15 L / min; the second gradient process parameters are: a laser power of 450 W, a scanning speed of 700 mm / min, a layer thickness of 50 μm, a substrate preheating temperature of 250 °C, and a protective gas flow rate of 15 L / min; the third gradient process parameters are: a laser power of 500 W, a scanning speed of 600 mm / min, a layer thickness of 60 μm, a substrate preheating temperature of 250 °C, and a protective gas flow rate of 15 L / min.

5. The method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology as described in claim 4, characterized in that, The first gradient mixed powder and the fifth gradient mixed powder each have 15 deposition layers, the second gradient mixed powder and the fourth gradient mixed powder each have 20 deposition layers, and the third gradient mixed powder has 25 deposition layers.

6. The method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology as described in claim 1, characterized in that, Step S2 further includes: before slicing the coil box model, dividing the coil box model into multiple sub-models along its circumference, and slicing each sub-model separately; In step S3, multiple coil box segments corresponding to the multiple sub-models are deposited and formed respectively, and the printed multiple coil box segments are spliced ​​and printed together.

7. The method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology as described in any one of claims 1-6, characterized in that, The stainless steel is composed of the following chemical elements by mass percentage: C: 0.01~0.03%, Si: 0.45~0.75%, Mn: 1.65~2.00%, Cr: 16.0~18.5%, Mo: 2.00~2.50%, Ni: 11.0~14.0%, Co: 0.07~0.1%; the balance being Fe and unavoidable impurities.

8. The method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology as described in claim 7, characterized in that, The first additive powder also includes TiC nanoparticles, and the volume of the TiC nanoparticles accounts for 1% to 10% of the volume of the first additive powder.

9. The method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology as described in claim 8, characterized in that, The average particle size of the first additive powder is 15μm to 45μm, and the average particle size of the second additive powder is 40μm to 60μm.

10. The method for manufacturing a stellarator superconducting magnet coil box based on additive manufacturing technology as described in any one of claims 1-6, characterized in that, In step S4, the temperature is raised to 800°C, and the hot isostatic pressing treatment is carried out under 100MPa argon gas conditions. Cool the product at temperatures ranging from -130°C to -196°C for 20-24 hours.

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