Additive manufacturing method for forming irregular capillary structure head of liquid rocket engine

Abstract

The present invention discloses a method for additive manufacturing of a deformed capillary head of a liquid rocket engine. The method includes the steps of: constructing an integrated head three-dimensional model; determining the growth direction of the head based on the integrated head three-dimensional model; realizing the optimization of the integrated head three-dimensional model based on the relevant parameters of the capillary determined according to the desired flow resistance and desired thermal resistance of the head, and obtaining an optimized three-dimensional model; determining the process support and the process powder outlet based on the growth direction of the head and the optimized three-dimensional model, and obtaining a process three-dimensional model of the head; determining the molding process of laser additive manufacturing; performing laser additive manufacturing molding through the process three-dimensional model and molding process of the head; removing the metal powder inside the workpiece, removing the process support by heat treatment; and chemically polishing the workpiece to obtain the head. According to the present invention, the precise molding of the entire deformed capillary head is achieved.

Description

[Technical field]

[0001] The present invention belongs to the technical field of additive manufacturing, and specifically relates to a high-precision additive manufacturing molding method for the contoured capillary head of a liquid rocket engine. [Background technology]

[0002] The head is the core part for completing the guidance and distribution of propellant in the gas generator and the thrust chamber of the attitude control engine and realizing the uniform distribution of propellant in the decomposition chamber. It contains a large number of capillary structures with a diameter of 0.6mm-0.8mm, a wall thickness of 0.1mm-0.2mm, and spatially irregular and twisted. At present, the attitude control head is manufactured by the traditional process of divided manufacturing + brazing, and the following problems mainly exist. 1, Poor consistency. The bending process of the capillary tube relies on manual labor, so the size consistency is poor, and the capillary tube needs to be adjusted after brazing, which affects the assembly of the product and the stability of the fluid pressure drop (drop). 2, Low reliability. The head is brazed with more than 20 parts such as capillaries, flanges, and ejection disks, and the quality control of the brazing is difficult, the strength of the welds is lower than the main body material, and the welds cannot be detected or measured. If the strength of the welds is insufficient during the work, the capillary tube may explode, and there is a large risk of thermal explosion, which affects the reliability of the engine. 3, The processing cycle is long. The manufacturing involves many specialties and processes, such as forging, heat treatment, surface treatment, machining, testing and assembly of parts, brazing, etc., and the entire production cycle takes two months, which is unfavorable to the reliable research and development production of the head.Additive manufacturing technology, as one of the latest and most advanced manufacturing technologies at present, has the characteristics of CAD / CAM integration, high efficiency and agile manufacturing, and provides a new solution to the design / manufacturing of attitude control engine heads with irregular capillary structures, but there are many factors that affect the molding, and there are technical problems such as immature technology and reduced product quality. Summary of the Invention

[0003] The purpose of the present invention is to provide an additive manufacturing molding method for a irregular capillary structure head of a liquid rocket engine in order to overcome the above-mentioned defects, and to solve the technical problems existing in the current traditional divided manufacturing + brazing combination process of attitude control engine head, such as poor consistency of the dimensional accuracy of the capillary structure, lack of reliability due to many welds that cannot be inspected or measured, high risk of thermal explosion, long processing cycle, etc. According to the present invention, the entire precise molding of the irregular capillary structure head can be realized.

[0004] In order to achieve the above object of the invention, the present invention provides the following technical means.

[0005] Step S1 of constructing an integrated head three-dimensional model; Step S2 of determining a growth direction of the head based on the integrated head three-dimensional model; Step S3: optimizing the integrated head three-dimensional model based on the relevant parameters of the capillary tube determined according to the desired flow resistance and the desired thermal resistance of the head to obtain an optimized three-dimensional model; Step S4: determining a process support and a process powder outlet according to the growth direction of the head and the optimized three-dimensional model, and obtaining a process three-dimensional model of the head; A step S5 of determining a forming process of laser additive manufacturing; Step S6 of performing laser additive manufacturing molding using the process 3D model of the head obtained in step S4 and the molding process obtained in step S5; Step S7: removing the metal powder from the inside of the workpiece obtained in step S6 and removing the process support by heat treatment; Step S8: chemically polishing the workpiece obtained in step S7 to obtain a head; A method for additive manufacturing of a shaped capillary structure head of a liquid rocket engine, comprising:

[0006] In addition, in step S1, the integrated head three-dimensional model includes a flange, a jet plate, a heat insulating frame, and a capillary tube, the flange and the jet plate are respectively located at both ends of the heat insulating frame, and a plurality of capillary tubes are integrated on the inner surface of the heat insulating frame, and both ends of the capillary tube are respectively connected to the flange and the jet plate; In step S2, based on the integrated head three-dimensional model, the growth direction of the head is determined according to the principles of minimum stress, minimum process support and removable, that is, the flange is connected to the substrate and arranged vertically.

[0007] In addition, in step S3, the method of optimizing the integrated head three-dimensional model based on the relevant parameters of the capillary tube determined according to the desired flow resistance and the desired thermal resistance of the head, and obtaining the optimized three-dimensional model includes the following steps: Step S3.1 of constructing a capillary shape compensation calculation formula for the capillary forming angle; Step S3.2 of constructing a head flow resistance calculation formula related to the capillary tube diameter and the capillary surface roughness; determining a diameter of the capillary tube and a surface roughness of the capillary tube according to a head flow resistance calculation formula based on a desired head flow resistance; Step S3.3: determining the number of capillaries, the distribution of capillaries, the forming angle of capillaries and the length of capillaries according to the desired thermal resistance of the head through a capillary shape compensation formula; Step S3.4: optimizing the head three-dimensional model based on the determined capillary diameter, capillary surface roughness, capillary number, capillary distribution, capillary forming angle and capillary length; Includes.

[0008] Further, in step S3.1, the method for constructing a capillary shape compensation calculation formula for the capillary forming angle includes: A series of capillaries whose forming angles change at equal intervals within a range of 0° to 60° and whose tube diameters change at equal intervals within a range of 0.4 to 1 mm are designed, and selective laser melting is performed using a series of three-dimensional head models including the series of capillaries; The collapse information of the hanging part of the capillary at each forming angle and each tube diameter is statistically obtained, and a capillary shape compensation calculation formula for the forming angle of the capillary is obtained by fitting the information; The forming angle is the angle between the inner surface of the capillary and a horizontal plane; The capillary shape compensation formula is:

number

number

[0009] Further, in step S5, the method includes determining process parameters of a capillary padding scan to improve the dimensional accuracy of the capillary; The process parameters include: spot 38-42 um, layer thickness 0.01-0.03 mm, laser power 90-120 W, scan speed 600-800 mm / s, line spacing 0.09-0.10 mm, and phase angle 67°.

[0010] In addition, in step S5, the method further includes performing a border scan at the edge of the padding scan trajectory of the vertical capillary to optimize the surface quality of the vertical capillary, specifically, First, a sub-peripheral scanning is performed using a laser having a relatively high energy, and then a peripheral scanning is performed using a laser having a relatively low energy, The process parameters for the sub-periphery scanning were laser power 50W and scanning speed 600mm / s. The process parameters for peripheral scanning were laser power 80 w and scan speed 400 mm / s. The diameter of the sub-circumferential scan is greater than the diameter of the peripheral scan.

[0011] Further, in step S5, the method further includes determining scanning parameters of the upper and lower surfaces to optimize the upper and lower surfaces formed in the additive manufacturing process; the upper surface being the excess surface of the previous layer relative to the next layer to be molded, and the lower surface being the excess surface of the next layer to be molded relative to the previous layer; The scanning parameters for the top surface were laser power 80-120w and scan speed 350-450mm / s. The scanning parameters for the lower surface are laser power 120-160W and scan speed 2500-2700mm / s.

[0012] Further, in step S4, the process support includes a solid support structure and a hollow columnar support structure; The lower end of the solid support structure is connected to the upper surface of the flange, the upper end of the solid support structure is connected to the lower end of the hollow columnar support structure, and the upper end of the hollow columnar support structure is connected to the lower surface of the ejection plate, the solid support structure is at 45° to the vertical direction, the hollow columnar support structure is arranged along the vertical direction, and the length of the hollow columnar support structure is 10 to 20 mm; The upper end of the solid support structure is provided with a diamond shaped hole.

[0013] Further, in step S4, a process powder outlet is located at the lowest part of a sealed chamber formed by the flange and the base plate, and a lower end of the capillary tube is connected to the process powder outlet; In step S7, the method for removing the metal powder inside the workpiece obtained in step S6 is to blow in high-pressure gas of 1.2-1.5 MPa from the upper end of the capillary tube and blow off the metal powder from the process powder outlet; In step S7, the method of removing the process support by heat treatment is to keep the temperature at 900-1000 ° C for 3-4 hours, and then remove the solid support by wire cutting; The wire cutting is performed using a high-speed reciprocating wire electric discharge machine, with a pulse width of 10-15 μs, a pulse interval of 100-120 μs, and a rectangular pulse waveform.

[0014] Furthermore, the additive manufacturing method for the irregular capillary structure head of the liquid rocket engine described above includes the steps of: S9: Perform a liquid flow test on the head to determine whether the head's flow resistance meets the desired flow resistance; The method further includes a step of detecting unnecessary objects in the head by a micro focus CT and determining whether or not metal powder remains inside the head; The parameters of the microfocus CT detection are voltage 240-290KV, current 280-330uA, detector sensitivity 2-4, exposure time 500-1000ms, resolution voxel size 70um, and the light direction is perpendicular to the vertical step of the capillary tube.

[0015] The present invention has at least one of the following beneficial effects compared to the prior art: (1) The additive manufacturing technology of the present invention has achieved an innovation in the design of the attitude control head with a special-shaped capillary structure. The external capillary of the conventional head is integrated into an insulating frame and optimized into an internal type, thereby solving the problems of low consistency, low rigidity, vibration during engine machining operation, effects of thermal expansion, and high risk of thermal explosion caused by the manual bending process of the conventional high aspect ratio external capillary. (2) In the present invention, by optimizing dimensional accuracy through the process of small spot and small layer thickness, optimizing shape accuracy through compensation of inclined capillary cut surface shape, and optimizing surface quality through vertical surface, upper / lower surface scanning strategy and process parameter control, the high precision, high surface quality and high consistency manufacturing of irregular capillary structure head is realized, and the problems of low consistency and low pass rate of head caused by manual bending, soldering deformation and manual maintenance are solved. (3) In the present invention, the risk of head waste is eliminated by detecting waste objects in the capillary tube using high-precision microfocus CT, and the reliability of the product is guaranteed. (4) In the present invention, by designing a lightweight support structure, it is ensured that the structure has a stable support function while being easily removable. (5) In the present invention, a method for controlling the liquid flow resistance of an additive manufacturing head is obtained through the technological path of head capillary diameter-surface quality-fluid pressure drop iterative optimization design, that is, the head flow resistance is controlled by adjusting the capillary diameter and surface quality. A method for controlling the thermal resistance of an additive manufacturing head is obtained through the technological path of capillary number / distribution / length-thermal resistance iterative optimization design, that is, the head thermal resistance is controlled by adjusting the capillary diameter size, number and distribution. (6) In the present invention, the manufacturing method for the flow resistance and thermal resistance of the additive manufacturing head can obtain the tube diameter size, number, length and distribution of the capillary structure of the additive manufacturing head that meets the design requirements, and realizes the design and manufacturing of the structure and function integration of the irregular capillary head. By integrating and manufacturing more than 30 parts in the traditional processing process of "machining + bending + chemical milling + brazing + welding", the problems existing in the traditional processing process such as many welds that cannot be inspected or measured, lack of reliability, long processing cycle, and many steps are solved. (7) The present invention provides a number of relevant calculation formulas that can comprehensively consider various influencing factors to achieve thermal resistance control and flow resistance control, which has universal applicability, effectively improves the efficiency of product design, and optimizes the thermal resistance and flow resistance performance of the product. In addition, a shape compensation method for the inclined step of the capillary tube is provided to avoid the occurrence of collapse and improve the quality of the product. (8) In the present invention, by designing the circulating flow chemical polishing tool and controlling the polishing process parameters, uniform and effective polishing of the additive manufacturing capillary is achieved, the head fluid pressure drop requirements are guaranteed, and the powder stuck to the head capillary is removed to ensure the reliability of the product. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is a schematic diagram of the overall head design structure of the present invention. [Diagram 2] FIG. 2 is a schematic diagram of surface roughness formation in a capillary structure. [Diagram 3] FIG. 2 is a schematic diagram of the outer and sub-outer perimeter scanning strategy of the present invention. [Figure 4]1 is a schematic diagram of the upper and lower surfaces of the present invention; [Diagram 5] FIG. 2 is a schematic diagram of an optimized three-dimensional model of a capillary structure head according to the present invention. [Figure 6] FIG. 1 is a schematic diagram of a process support structure of the present invention. [Figure 7] 1 shows the shape of the inclined portion of the capillary of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention will now be described in detail, and the features and advantages of the present invention will become more apparent from the description.

[0018] As used herein, the term "exemplary" means "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" should not be construed as superior or better than other embodiments. While aspects of the embodiments are illustrated in the drawings, the drawings are not necessarily drawn to scale unless otherwise indicated.

[0019] The additive manufacturing method for the profiled capillary structure head of a liquid rocket engine according to the present invention includes the following steps. Step (1): Build a 3D model of the integrated head by additive manufacturing. Step (2): Based on the stress distribution and support configuration during the molding process of the integrated model obtained in step (1), determine the growth direction of the head according to the principles of minimum stress, minimum support and detachability. Step (3): Based on the growth direction in step (2), extract typical structures in the model, i.e., characteristic capillaries, and optimize the accuracy and surface quality of the capillary structures to obtain capillary process parameters and scan paths with high accuracy and high surface quality. Step (4): The process,iteratively optimizes the design and obtains an optimized,3D model. Step (5): Based on the 3D model determined in step (4) and the growth direction determined in step (2), design the process support and the process powder outlet, and obtain a process 3D model of the head. Step (6): Using the process parameters and scan speed obtained in step (3), slice the process 3D model obtained in step (5), obtain the laser scan path parameters for each sliced ​​layer, and perform laser additive manufacturing molding. Step (7): The metal powder in the head capillary structure obtained in step (6) is removed, and after heat treatment, the process support is removed. Step (8): After the head obtained in step (7) is subjected to a chemical polishing process, a liquid flow test is performed. Step (9): Detect unwanted objects on the capillary structure head obtained in step (8) using microfocus CT.

[0020] In step (1), the characteristic configuration of the irregular capillary structure, for example, the attitude control engine head, includes a flange, a blowout plate, a heat insulating frame, and a capillary. In the conventional capillary structure head, the capillary with a high aspect ratio is exposed and distributed independently between the blowout plate, the flange, and the heat insulating frame, and has a weak rigidity, and there is a high risk of thermal explosion due to the influence of vibration and thermal expansion during the operation of the engine. By utilizing the flexible characteristics of the process design of additive manufacturing, the capillary structure is integrated into the heat insulating frame, thereby improving the rigidity and reliability of the capillary, and achieving the overall design of additive manufacturing (FIG. 1).

[0021] In the step (2), the head growth direction is determined according to the principles of minimum stress, minimum support and removable based on the stress distribution and support configuration during the molding process. The big end flange is connected to the base and arranged vertically.

[0022] In the step (3), characteristic capillaries, which are typical structures in the model, are extracted, and the accuracy of the capillary structure and the surface quality are optimized.

[0023] (3-1) Optimization of capillary precision The optimization of accuracy includes optimization of dimensional accuracy and optimization of shape accuracy. Regarding the optimization of dimensional accuracy, the dimensional accuracy of the part is mainly affected by the width of the melt passage and the thickness of the sliced ​​layer, and the width of the melt passage is determined by the size of the laser spot. The normal spot diameter is 80-100um, but in the present invention, the capillary tube is formed with process parameters of a small spot of 40um and a small layer thickness of 0.02mm. The small spot reduces the width of the melt passage, and the small layer thickness reduces the staircase effect of the slice, thereby achieving high-precision formation of the capillary tube. The process parameters for the small spot of 40um and the small layer thickness of 0.02mm are laser power 90-120W, scan speed 600-800mm / s, line spacing 0.09-0.10mm, and phase angle 67°.

[0024] The optimization of shape accuracy mainly includes two steps. In the first step, a series of capillary structures with forming angles of 0°, 20°, 30°, 40°, 50° and tube diameters of 0.4mm-1mm (increasing by 0.1mm) are designed and selective laser melting is performed. The forming angle refers to the angle between the inner surface of the capillary and the horizontal. In the second step, the collapse distance and collapse shape of the hanging part of the capillary at each forming angle and each tube diameter are statistically analyzed, and a shape compensation calculation formula for different tube diameters and different forming angles is obtained by fitting.

number

[0025] (3-2) Optimization of surface quality The surface quality optimization includes optimization of the vertical surface quality and optimization of the top and bottom surfaces. The vertical surface refers to a surface with a forming angle of 90°. In order to obtain a smooth surface, it is necessary to eliminate the sawtooth contour caused by the melt passage and reduce the powder adhesion phenomenon. The present invention improves the quality of the vertical surface by border scanning the edge (actual contour in FIG. 3) of the padding scanning trajectory. The border scanning includes the outer periphery (outer periphery in FIG. 3) and the sub-periphery (additional periphery in FIG. 3). That is, first, a sub-periphery scanning is performed using a laser with a relatively high energy to eliminate the error of the sawtooth contour, and then a peripheral scanning is performed using a laser with a relatively low energy to reduce the powder adhesion situation on the surface. The additional periphery overlaps with the contour of the slice, so that the error caused by the slice is eliminated. 30% to 50% of the outer circumference overlaps with the additional outer circumference (overlap area in FIG. 3; FIG. 2), so by designing the sub-periphery and the outer circumference path and setting their energy density, the sawtooth error is eliminated, the powder adhesion phenomenon on the surface is reduced, and the quality of the vertical surface of the capillary structure is improved. The sub-periphery process parameters are laser power 50W and scan speed 600mm / s. The outer circumference process parameters are laser power 80W and scan speed 400mm / s. For the vertical hole with a forming angle of 90°, a border scan can be performed at the edge of the padding scan trajectory to eliminate the sawtooth profile caused by the melt passage as shown in FIG. 2, reduce the powder adhesion phenomenon, and obtain a smooth inner hole surface.

[0026] The upper surface is the extra surface of the previous layer for the next layer to be formed, and the lower surface is the extra surface of the next layer to be formed for the previous layer. The schematic diagram is shown in FIG. 4. For the upper surface, the growth support point is solidly formed, so the molten pool collapse and dross adhesion phenomenon do not occur, and the surface is smoothed by setting a relatively high energy density. For the lower surface, the growth support point is loose powder, so the molten pool collapse and dross adhesion phenomenon occur during the forming process, and the problems of molten pool collapse, dross adhesion, and surface quality degradation caused by powder adhesion on the surface can be solved by setting a relatively low energy density. The parameters of the upper surface are upper surface laser power 100W, scan speed 400mm / s, and the parameters of the lower surface are lower surface laser power 140W, scan speed 2600mm / s.

[0027] In step (4), the head structure-function integration design model is obtained by optimizing the head structure-function integration design model based on the additive manufacturing flow resistance and thermal resistance control method, i.e., the capillary diameter-surface quality-fluid pressure drop iterative optimization design and the head capillary number / distribution / length-thermal resistance iterative optimization design (Figure 5).

[0028] In this step, based on the integrated head design, the capillary structure's tube diameter size, number, distribution, etc. are iteratively designed to form a control method for the head's liquid flow resistance and thermal resistance, and finally, a head structure-function integrated design model is obtained through optimization based on the flow resistance and thermal resistance control method. The head flow resistance control technology path is the head capillary tube diameter-surface quality-fluid pressure drop iterative optimization design, and the head thermal resistance control technology path is the capillary number / distribution / length-thermal resistance iterative optimization design.

[0029] (4.1) Iterative optimization of head capillary diameter-surface quality-fluid pressure drop The iterative optimization method of head capillary tube diameter-surface quality-fluid pressure drop mainly includes three steps. First step: Design a series of capillary structure heads with tube diameters of 0.4mm-1mm and increasing by 0.1mm. Second step: Chemical polishing is performed for different times (0.5min, 1min, 2min, 3min) for each tube diameter head, and the capillary surface roughness at different chemical polishing times is measured using a 3D digital microscope. Third step: Measure the head fluid pressure drop and pressure drop uniformity in different regions for different tube diameters and different surface roughness, and statistically analyze the data, and fit to determine the corresponding relationship of head capillary tube diameter-surface roughness-fluid pressure drop. Step 4: Design a series of capillary structure heads with tube diameters of 0.4mm-1mm and increasing by 0.05mm, carry out chemical polishing with different process parameters (1mm, 1.5min, 2.5min, 2min, 3min), conduct fluid pressure drop and uniformity tests, correct and verify the correspondence equation of the head capillary tube diameter-surface roughness-fluid pressure drop fitted in step 3, and finally determine the calculation equation for the head fluid pressure drop (below).

number

[0030] Based on the above head fluid pressure drop calculation formula, according to the head design pressure drop requirements, calculate the capillary tube diameter and surface roughness to obtain the capillary tube size and surface condition, where the tube diameter is 0.4 mm and the chemical polishing time is 3 min.

[0031] Capillary head chemical polishing is affected by the capillary structure and the blocking force of the solution flow. The solution exchange action in the capillary is weak, and after polishing for a while, the concentration of the chemical solution is relatively low, and there is a concentration difference in each part, which causes insufficient or uneven chemical milling polishing. In order to ensure uniform and smooth polishing of the capillary, a solution circulation flow chemical milling finishing tool-a flow guide plate tool (a hole with a diameter that matches the diameter of the top of the head is formed in the central area of ​​the tool, and a screw hole with a diameter of 5 mm is formed at each of the four corners, and the tool and the top of the head are sealed connected by bolts, and the pump is connected to the head by a pipe) is designed, and the polishing solution is uniformly filled into the capillary at a certain pressure and speed by the electric pump, which ensures the uniformity of the exchange of the chemical solution. Here, the pump pressure is 0.7Mpa, and the solution flow speed is 50-60mm / s. The chemical polishing solution is a mixture of hydrochloric acid, nitric acid, hydrofluoric acid, etc., in a ratio of 4:3:1. The polishing removal amount for the polishing times of 0.5 min, 1 min, 2 min, and 3 min is less than 0.05 mm, and does not affect the strength of the head.

[0032] (4.2) Number / distribution / length of capillaries - Iterative optimization design of thermal resistance In additive manufacturing of capillary structure head, the independently distributed capillaries in the traditional design scheme are integrated into the heat insulation frame, so that the thermal resistance of the head is relatively small. The design of large flow rate, high integration and high aspect ratio enhances the cooling, reduces the heat intrusion heat conduction area, and increases the heat conduction distance, thereby improving the thermal resistance of the additive manufacturing capillary head. Through multiple capillary number / distribution / length-thermal resistance iterative designs, the number, distribution and length information of the head capillaries with thermal resistance requirements can be obtained. That is, the number of capillaries is 39 in total, which are concentrated and distributed in the heat insulation frame and are divided into four types: A, B, C and D. The four types of irregular capillaries, A, B, C and D, are distributed in a ring shape. The A irregular capillaries are distributed on the outermost circumference, with a total of 18, the development length is 160 mm, and the forming angle of the capillaries in the inclined section is 20°. The capillaries B, C, and D are distributed toward the center in order, with 12 capillaries B, the developed length is 150 mm, and the capillary forming angle of the inclined part is 23°. There are 6 capillaries C, the developed length is 140 mm, and the capillary forming angle of the inclined part is 26°. There are 3 capillaries D, the developed length is 120 mm, and the capillary forming angle of the inclined part is 28°. Using the capillary shape compensation parabola calculation formula in step (3), calculate the shapes of the capillary inclined parts for the four types of tube diameters A, B, C, and D (Figure 7).

[0033] Through iterative optimization of head capillary tube diameter-surface quality-fluid pressure drop, and iterative optimization design of capillary number / distribution / length-thermal resistance, the final optimized 3D model of the capillary structure head is determined (Figure 5).

[0034] In step (5), in the growth direction determined in step (2), the bottom surface of the upper head is in a suspended state, so it is necessary to design and support it with an additive manufacturing auxiliary process. From the three perspectives of ensuring smooth molding, controlling the temperature field heat transfer and stress, and making it easy to remove, a solid + hollow columnar combination support is designed, which ensures stability and deformation control during the molding process through the solid support, and makes it easy to remove through the hollow columnar support. In the solid + hollow columnar combination support, the solid support structure is a 45° self-supporting molding structure, which is at an angle of 45° to the axis. This allows it to fall onto the plane of the ejection platen and avoids falling onto the arc surface with capillary features. In addition, a diamond hole is designed in the support to ensure strength while achieving a lightweight design (Figure 6). The hollow columnar support has an outer diameter of 1.23 mm and a wall thickness of 0.2 mm, and is installed on the suspended surface of the ejection platen, and falls onto the self-supporting solid support, making it easy to remove the support.

[0035] In step (7), after the selective laser melting is completed, the powder material is filled into the capillary. In order to ensure that the powder in the capillary is completely removed, the bottom part of the sealed chamber consisting of the bottom flange of the head and the base plate is provided with 18 process powder outlets distributed along the circumference, and the powder outlets are connected at the bottom of the flange to improve the openness of the structure, and the upper and lower ports of each capillary are ensured to be connected, so that the powder in the capillary can be smoothly blown out by compressed air. The process powder outlet is semicircular in shape and has a radius of 2 mm.

[0036] In step (7), the powder is completely removed from the process powder outlet by blowing it out of the capillary inlet on the blowing plate using high pressure gas of 1.2-1.5Mpa. The heat treatment is a homogenization heat treatment, which is kept at a temperature of 900-1000°C for 3h and then cooled by air to remove the thermal stress in the head forming process, adjust the structure and performance, and meet the design requirements. The solid support is removed by wire cutting, and the columnar support is removed by grinding. Here, the wire cutting is wire cutting using a high speed reciprocating wire electric discharge machine, the pulse width is set to 10-15μs, the pulse interval is 100-120μs, and the waveform is a square wave pulse.

[0037] In step (9), the capillary structure head is subjected to detection of unwanted objects by microfocus CT. The detection parameters of the microfocus CT are voltage 240-290 KV, current 280-330 uA, detector sensitivity 2-4, exposure time 500-1000 ms, resolution voxel size 70 um, and the light direction is perpendicular to the capillary tube of the vertical step.

[0038] The present invention has been described in detail above through specific embodiments and examples, but these descriptions do not limit the present invention. Those skilled in the art can make various equivalent substitutions, modifications or improvements to the technical means of the present invention and its embodiments without departing from the spirit and scope of the present invention. All of these are included in the scope of the present invention. The protection scope of the present invention is subject to the scope of the attached claims.

[0039] The contents not described in detail in the present specification are common knowledge in the art.

Claims

1. 1. A method for additive manufacturing of a contoured capillary head of a liquid rocket engine, comprising: Step S1 of constructing an integrated head three-dimensional model; Step S2 of determining a growth direction of the head based on the integrated head three-dimensional model; Step S3: optimizing the integrated head three-dimensional model based on the relevant parameters of the capillary tube determined according to the desired flow resistance and the desired thermal resistance of the head to obtain an optimized three-dimensional model; Step S4: determining a process support and a process powder outlet according to the growth direction of the head and the optimized three-dimensional model, and obtaining a process three-dimensional model of the head; A step S5 of determining a forming process of laser additive manufacturing; Step S6 of performing laser additive manufacturing molding using the process 3D model of the head obtained in step S4 and the molding process obtained in step S5; Step S7: removing the metal powder from the inside of the workpiece obtained in step S6 and removing the process support by heat treatment; Step S8: chemically polishing the workpiece obtained in step S7 to obtain a head; A method for additive manufacturing of a contoured capillary structure head of a liquid rocket engine, comprising:

2. In step S1, the integrated head three-dimensional model includes a flange, a jet plate, a heat insulating frame, and a capillary tube, the flange and the jet plate are respectively located at both ends of the heat insulating frame, and a plurality of capillary tubes are integrated on the inner surface of the heat insulating frame, and both ends of the capillary tube are respectively connected to the flange and the jet plate; The additive manufacturing molding method for the irregular capillary structure head of a liquid rocket engine as described in claim 1, characterized in that in step S2, based on the integrated head three-dimensional model, the growth direction of the head is determined according to the principles of minimum stress, minimum process support and removable, i.e., the flange is connected to the substrate and arranged vertically.

3. In step S3, the method for optimizing the integrated head three-dimensional model and obtaining the optimized three-dimensional model based on the relevant parameters of the capillary tube determined according to the desired flow resistance and the desired thermal resistance of the head is as follows: Step S3.1 of constructing a capillary shape compensation formula for the capillary forming angle; Step S3.2 of constructing a head flow resistance calculation formula related to the capillary diameter and the capillary surface roughness; determining a diameter of the capillary tube and a surface roughness of the capillary tube according to a head flow resistance calculation formula based on a desired head flow resistance; Step S3.3: determining the number of capillaries, the distribution of capillaries, the shaping angle of capillaries and the length of capillaries according to the desired thermal resistance of the head through a capillary shape compensation formula; Step S3.4: optimizing the head three-dimensional model according to the determined capillary diameter, capillary surface roughness, capillary number, capillary distribution, capillary forming angle and capillary length; The additive manufacturing method for the contoured capillary structure head of a liquid rocket engine according to claim 1, comprising:

4. In step S3.1, the method for constructing a capillary shape compensation equation for the capillary shaping angle includes: A series of capillaries having a forming angle that changes at equal intervals within a range of 0° to 60° and a tube diameter that changes at equal intervals within a range of 0.4 to 1 mm are designed, and selective laser melting is performed using a series of three-dimensional head models including the series of capillaries; The collapse information of the hanging part of the capillary at each forming angle and each tube diameter is statistically obtained, and a capillary shape compensation calculation formula for the forming angle of the capillary is obtained by fitting the information; The forming angle is the angle between the inner surface of the capillary and a horizontal plane; The capillary shape compensation formula is: [0010] where θ is the forming angle of the capillary and d ０ is the capillary diameter compensation value, In step S3.2, the method for constructing a head flow resistance calculation formula related to the capillary diameter and the capillary surface roughness is as follows: Designing a series of capillaries whose diameters change at equal intervals within a range of 0.4 to 1 mm, and performing selective laser melting using a series of head three-dimensional models including the series of capillaries to obtain a series of heads having different capillary diameters; Until all the chemical polishing for the heads with different capillary diameters is completed, chemical polishing is performed for different times for the heads with the same capillary diameter; The surface roughness of the capillary tubes was measured with a 3D digital microscope after different chemical polishing times. The head flow resistance calculation formula for the capillary diameter and capillary surface roughness is calculated by measuring the fluid pressure drop and the uniformity of the fluid pressure drop for each head, including different tube diameters and different surface roughnesses, and fitting the formula: [0025] Get where P is the pressure drop, d is the diameter of the capillary tube, and R is the surface roughness of the capillary tube. The additive manufacturing method for a irregular capillary structure head of a liquid rocket engine as described in claim 3, characterized in that in step S3.3, the number of capillaries determined based on the desired flow resistance of the head is 30-100, the distribution of the capillaries is a plurality of concentric circles, the same capillary includes a vertical step and an inclined step, the molding angles of the inclined steps of the capillaries distributed in the same concentric circle are the same, the molding angles of the inclined steps of the capillaries distributed in different concentric circles increase from the outside to the inside, the lengths of the capillaries distributed in different concentric circles decrease from the outside to the inside, and the tube diameters of the inclined steps of the capillaries are optimized according to a capillary shape compensation calculation formula.

5. In step S5, determining process parameters for capillary padding scan to improve the dimensional accuracy of the capillary; The additive manufacturing method for the irregular capillary structure head of a liquid rocket engine according to claim 1, characterized in that the process parameters include: spot 38-42um, layer thickness 0.01-0.03mm, laser power 90-120W, scan speed 600-800mm / s, line spacing 0.09-0.10mm, and phase angle 67°.

6. In step S5, the method further includes performing a border scan at the edge of the padding scan trajectory of the vertical capillary to optimize the surface quality of the vertical capillary, specifically, First, a sub-peripheral scanning is performed using a laser having a relatively high energy, and then a peripheral scanning is performed using a laser having a relatively low energy, The process parameters for the sub-periphery scanning were a laser power of 50 W and a scanning speed of 600 mm / s. The process parameters for the peripheral scanning were a laser power of 80 w and a scanning speed of 400 mm / s. The additive manufacturing method for the irregular capillary structure head of a liquid rocket engine according to claim 5, characterized in that the diameter of the sub-circumferential scan is larger than the diameter of the peripheral scan.

7. In step S5, the method further includes determining scanning parameters of the upper and lower surfaces to optimize the upper and lower surfaces formed in the additive manufacturing process; the upper surface being the excess surface of the previous layer relative to the next layer to be molded, and the lower surface being the excess surface of the next layer to be molded relative to the previous layer; The scanning parameters for the top surface are laser power 80-120 w and scan speed 350-450 mm / s; The additive manufacturing molding method for the irregular capillary structure head of a liquid rocket engine according to claim 6, characterized in that the scanning parameters of the lower surface are: laser power 120-160W, scanning speed 2500-2700mm / s.

8. In step S4, the process support includes a solid support structure and a hollow columnar support structure; The lower end of the solid support structure is connected to the upper surface of the flange, the upper end of the solid support structure is connected to the lower end of the hollow columnar support structure, and the upper end of the hollow columnar support structure is connected to the lower surface of the ejection disk, the solid support structure is at 45° to the vertical direction, the hollow columnar support structure is arranged along the vertical direction, and the length of the hollow columnar support structure is 10-20 mm; The additive manufacturing method for the irregular capillary structure head of a liquid rocket engine as claimed in claim 2, characterized in that: the upper end of the solid support structure is provided with a diamond-shaped hole.

9. In step S4, the process powder outlet is located at the lowest part of the sealed chamber formed by the flange and the base plate, and the lower end of the capillary tube is connected to the process powder outlet; In step S7, the method of removing the metal powder inside the workpiece obtained in step S6 is to blow in high-pressure gas of 1.2-1.5 MPa from the upper end of the capillary tube and blow off the metal powder from the process powder outlet; In step S7, the method of removing the process support by heat treatment is to keep the temperature at 900-1000°C for 3-4 hours, and then remove the solid support by wire cutting. The additive manufacturing molding method for the irregular capillary structure head of a liquid rocket engine as described in claim 2, characterized in that the wire cutting is wire cutting using a high-speed reciprocating wire electric discharge machine, the pulse width is 10-15 μs, the pulse interval is 100-120 μs, and the waveform is a rectangular wave pulse.

10. S9: Perform a liquid flow test on the head to determine whether the head's flow resistance meets the desired flow resistance; The method further includes a step of detecting unnecessary objects in the head by microfocus CT and determining whether or not metal powder remains inside the head; The additive manufacturing molding method for the irregular capillary structure head of a liquid rocket engine according to claim 1, characterized in that the parameters of the microfocus CT detection are: voltage 240-290 KV, current 280-330 uA, detector sensitivity 2-4, exposure time 500-1000 ms, resolution voxel size 70 um, and the light beam direction is perpendicular to the vertical step of the capillary tube.

Images