Method for laser powder bed fusion forming of large-aspect-ratio cobalt-based superalloy dual-element nozzles

Abstract

The application discloses a large-length-diameter-ratio cobalt-based high-temperature alloy double-component nozzle laser selective melting forming method, which comprises the following steps: determining a three-dimensional model corresponding to a large-length-diameter-ratio cobalt-based high-temperature alloy double-component nozzle; carrying out process allowance design on the three-dimensional model to obtain a manufacturing model; simulating and analyzing stress / strain distribution in a manufacturing process of the manufacturing model by using different cobalt-based high-temperature alloy laser selective melting forming process parameters to determine final manufacturing process parameters; carrying out slice processing on the manufacturing model and placing the final manufacturing process parameters into the manufacturing model to obtain laser scanning path data of each slice layer; forming the double-component nozzle based on the obtained laser scanning path data of each slice layer; blowing off floating powder on inner and outer surfaces of the double-component nozzle, carrying out stress relief heat treatment, and then carrying out linear cutting separation on the substrate and the double-component nozzle. The application solves problems of long deep hole manufacturing cycle, easy deformation of slender rods in machining, low machining efficiency and low qualified rate and the like in traditional manufacturing processes.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal additive manufacturing, and particularly relates to a large-length-diameter-ratio cobalt-based high-temperature alloy double-component nozzle laser selective melting forming method. BACKGROUND

[0002] The thrust chamber is one of the most critical components of a reusable full-flow staged combustion cycle liquid rocket engine, the thrust chamber injector structure is complex, and the core component of the injector, the cobalt-based high-temperature alloy double-component internal mixing nozzle, is subjected to long-term repeated flushing of high-temperature gas rich in oxygen and fuel on the inside and outside during service, which puts extremely high requirements on the structural integrity, performance and dimensional consistency of the large-length-diameter-ratio nozzle under the condition of reuse. The current engine thrust chamber nozzle length-diameter ratio is usually 10-20, which is usually composed of two internal and external nozzles by brazing or high-energy beam welding, and the performance of the weld of the traditional segmented nozzle is prone to fluctuation during subsequent manufacturing and thermal service, and there is a risk of failure during reuse. The thrust chamber nozzle length-diameter ratio of the reusable full-flow staged combustion cycle liquid rocket engine reaches more than 40, which has a lower design structure stiffness than the traditional nozzle and is difficult to process using the traditional processing method, and the process is complex and the scrap rate is high.

[0003] The laser selective melting forming technology has the advantages of digitization, ability to manufacture complex parts, high manufacturing efficiency, etc., and provides a new solution for the high-efficiency manufacturing of the large-length-diameter-ratio cobalt-based high-temperature alloy nozzle. The nozzle has a slender structure and has extremely high requirements on coaxiality and cylindricity, and due to the periodic rapid heating and cooling during the laser selective melting forming process, a high temperature gradient and thermal stress are easily generated, which eventually leads to bending deformation of the product, affecting the dimensional accuracy, and a new laser selective melting forming scheme needs to be designed. SUMMARY

[0004] The technical problem of the application is to overcome the shortcomings of the prior art and provide a large-length-diameter-ratio cobalt-based high-temperature alloy double-component nozzle laser selective melting forming method, which aims to solve the problems of long deep hole manufacturing cycle, easy deformation of slender rods during processing, low processing efficiency and low pass rate in the traditional manufacturing process.

[0005] To solve the above technical problems, the application discloses a large-length-diameter-ratio cobalt-based high-temperature alloy double-component nozzle laser selective melting forming method, which comprises the following steps:

[0006] determining a three-dimensional model corresponding to the large-length-diameter-ratio cobalt-based high-temperature alloy double-component nozzle;

[0007] designing a process allowance for the three-dimensional model corresponding to the large-length-diameter-ratio cobalt-based high-temperature alloy double-component nozzle to obtain a manufacturing model;

[0008] The stress / strain distribution in the manufacturing model manufacturing process is simulated and analyzed by using different cobalt-based superalloy laser selective melting forming process parameters, and according to the stress / strain distribution results, a group of cobalt-based superalloy laser selective melting forming process parameters with the minimum deformation is selected as the final manufacturing process parameters;

[0009] The manufacturing model is sliced and the final manufacturing process parameters are put in to obtain the laser scanning path data of each slice layer;

[0010] The obtained laser scanning path data of each slice layer is imported into the applicable laser selective melting forming equipment, a stainless steel substrate is installed, the forming chamber is replaced with an inert gas environment, cobalt-based superalloy powder is used, and a double-element nozzle is formed.

[0011] After laser selective melting forming, the floating powder on the inner and outer surfaces of the double-element nozzle is blown off, stress relief heat treatment is carried out, and the substrate and the double-element nozzle are separated by wire cutting.

[0012] In the above-mentioned large-length-diameter-ratio cobalt-based superalloy double-element nozzle laser selective melting forming method, the length of the large-length-diameter-ratio cobalt-based superalloy double-element nozzle is 250mm-400mm, the diameter is Φ5mm-Φ10mm, and the circumferential hole diameter is Φ1.0mm-Φ5.0mm.

[0013] In the above-mentioned large-length-diameter-ratio cobalt-based superalloy double-element nozzle laser selective melting forming method, the process allowance includes product shrinkage compensation allowance and machining allowance; wherein the product shrinkage compensation allowance is to design a 0.12% scaling amount for the three-dimensional model corresponding to the large-length-diameter-ratio cobalt-based superalloy double-element nozzle.

[0014] In the above-mentioned large-length-diameter-ratio cobalt-based superalloy double-element nozzle laser selective melting forming method, the cobalt-based superalloy laser selective melting forming process parameters include layer thickness, laser scanning spacing, laser power, laser scanning speed, phase angle, and nozzle root fillet in contact with the substrate.

[0015] In the above-mentioned large-length-diameter-ratio cobalt-based superalloy double-element nozzle laser selective melting forming method, the size precision of the large-length-diameter-ratio cobalt-based superalloy double-element nozzle obtained after laser selective melting forming is ±0.1mm, the inner and outer surface cylindricity of the nozzle is ≤0.1mm, the coaxiality is ≤0.1mm, and the surface roughness Ra is 6.3μm.

[0016] The present application has the following advantages:

[0017] (1) The application discloses a large-length-diameter-ratio cobalt-based high-temperature alloy double-component nozzle laser selective melting forming method, which can directly and integrally manufacture products through a three-dimensional model of the large-length-diameter-ratio cobalt-based high-temperature alloy double-component nozzle, especially can directly manufacture fine structures such as throttle holes, inner-outer nozzle interlayers and retraction chambers, and omits multiple processes such as electrical processing, machining, brazing and high-energy beam welding, saves complex process equipment such as electrical spark electrodes and high-energy beam welding fixtures, and eliminates the influence of subsequent processing, welding and service heat processes on the inner-outer nozzle welds, so that the manufacturing process is greatly simplified and the efficiency is greatly improved, the nozzle required by each thrust chamber can be simultaneously manufactured in a same furnace batch, the product quality is high in consistency, the integrated efficient manufacturing of the large-length-diameter-ratio double-component nozzle is completely realized, and a key technical problem in the manufacturing of full-flow staged combustion cycle engines is solved.

[0018] (2) The application discloses a large-length-diameter-ratio cobalt-based high-temperature alloy double-component nozzle laser selective melting forming method, and the size precision of the large-length-diameter-ratio cobalt-based high-temperature alloy double-component nozzle obtained after laser selective melting forming can reach ±0.1 mm, the inner-outer surface cylindricity of the nozzle is ≤0.1 mm, the coaxiality is ≤0.1 mm, and the surface roughness can reach Ra6.3 μm, so as to avoid the bending deformation caused by the large-length-diameter-ratio structure characteristics of the nozzle in the manufacturing process, utilize stress / strain simulation analysis, select the processing parameters with the minimum stress / strain, and adopt a chessboard type scanning strategy of a laser scanning path, so as to slow down the stress concentration phenomenon in the nozzle manufacturing process, and realize the high-efficiency and high-precision laser selective melting forming of the large-length-diameter-ratio nozzle. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a three-dimensional view of a large-length-diameter-ratio cobalt-based high-temperature alloy double-component nozzle in the embodiment of the application;

[0020] Figure 2 is a sectional view of a large-length-diameter-ratio cobalt-based high-temperature alloy double-component nozzle in the embodiment of the application. DETAILED DESCRIPTION

[0021] In order to make the object, technical scheme and advantages of the application clearer, the following will further describe the disclosed embodiments of the application in combination with the drawings.

[0022] At present, the traditional manufacturing method of the large-length-diameter-ratio cobalt-based high-temperature alloy double-component nozzle is a multi-process composite processing of electrical spark, machining, brazing and high-energy beam welding, and the traditional manufacturing process has weak links such as long deep hole manufacturing cycle, deformation and over-difference of slender rod machining, low machining efficiency and low pass rate. Figure 1 and Figure 2 The application provides a large-length-diameter-ratio cobalt-based high-temperature alloy double-component nozzle laser selective melting forming method, which comprises the following steps:

[0023] Step 1, determining the three-dimensional model corresponding to the large aspect ratio cobalt-based superalloy double-element nozzle.

[0024] In this embodiment, according to the service condition requirements of the large aspect ratio cobalt-based superalloy double-element nozzle, the three-dimensional model corresponding to the nozzle is designed by using the modeling software UG. The length of the large aspect ratio cobalt-based superalloy double-element nozzle is 250mm-400mm, the diameter is Φ5mm-Φ10mm, and the circumferential hole diameter is Φ1.0mm-Φ5.0mm.

[0025] Step 2, process allowance design is performed on the three-dimensional model corresponding to the large aspect ratio cobalt-based superalloy double-element nozzle to obtain a manufacturing model.

[0026] In this embodiment, during the manufacturing process of the large aspect ratio cobalt-based superalloy double-element nozzle, the cobalt-based superalloy powder material undergoes the processes of laser heat source heat transfer, melting, cooling and solidification, and there are complex thermal stress and deformation in the thermal processing process, which can cause the shape to change. Some parts of the nozzle are joint surfaces and parts to be welded, which need to be machined to ensure the surface size precision and surface quality, so the three-dimensional model corresponding to the large aspect ratio cobalt-based superalloy double-element nozzle needs to be designed for process allowance to obtain a manufacturing model.

[0027] Preferably, the process allowance mainly includes product shrinkage compensation allowance and machining allowance. The product shrinkage compensation allowance is to design a 0.12% shrinkage amount for the three-dimensional model corresponding to the large aspect ratio cobalt-based superalloy double-element nozzle. The machining allowance is 0.5mm.

[0028] Step 3, different cobalt-based superalloy laser selective melting forming process parameters are used to simulate and analyze the stress / strain distribution in the manufacturing process of the manufacturing model, and according to the stress / strain distribution results, the cobalt-based superalloy laser selective melting forming process parameter group with the smallest deformation is selected as the final manufacturing process parameter.

[0029] In the present embodiment, the structural characteristics of easy bending deformation of the large aspect ratio cobalt-based superalloy dual-element nozzle formed by laser selective melting can be analyzed, and different cobalt-based superalloy laser selective melting forming process parameters (including but not limited to layer thickness, laser scanning spacing, laser power, laser scanning speed, phase angle, root fillet of nozzle and substrate contact, etc.) are designed. Further, different cobalt-based superalloy laser selective melting forming process parameters are used to simulate and analyze the stress / strain distribution in the manufacturing model manufacturing process, and the stress / strain characteristic values are obtained; the stress / strain characteristic values are input as a scatter plot, and the stress-strain curve formula is obtained by observing the scatter distribution; according to the simulation results, it is found that the stress distribution of the nozzle part is uniform and the strain generated when deformation occurs is uniform in the circumferential direction; finally, the cobalt-based superalloy laser selective melting forming process parameters with the smallest deformation amount are selected as the final manufacturing process parameters. For example, the final manufacturing process parameters obtained are as follows: layer thickness 0.03 mm, laser scanning spacing 0.10 mm, laser power 230-240 W, laser scanning speed 860-880 mm / s, phase angle 67°; an R=2 mm fillet is designed at the root of the nozzle and the substrate contact to enhance the connection strength of the nozzle and the substrate, and to avoid stress concentration and cracking risk.

[0030] Step 4, slice the manufacturing model and input the final manufacturing process parameters to obtain the laser scanning path data of each slice layer, i.e. the actual motion trajectory of the laser in the scanning area during the manufacturing process of each cross section.

[0031] Step 5, import the obtained laser scanning path data of each slice layer into the applicable laser selective melting forming equipment, install the stainless steel substrate, replace the forming chamber with an inert gas environment, use cobalt-based superalloy powder, and form a dual-element nozzle.

[0032] Step 6, after laser selective melting, blow off the floating powder on the inner and outer surfaces of the dual-element nozzle, perform stress relief heat treatment, and then perform linear cutting separation of the substrate and the dual-element nozzle.

[0033] In the embodiment, the inert gas is argon, the oxygen content in the manufacturing bin during the nozzle manufacturing process is required to be less than 500 PPM, and the powder amount in the powder box of the device is sufficient to complete the entire part processing at one time. In order to reduce the damage of the commonly used mechanical knocking to the nozzle structure, and at the same time ensure the cleaning effect, the loose powder in the nozzle is blown clean by using diversified non-damage tools, and the specific process is that the loose powder and surface floating powder in the nozzle obtained by laser selective melting are cleaned by using 0.6 Mpa-0.8 Mpa compressed air combined with an ultrasonic vibration platform; the stress relief heat treatment system is: vacuum solid solution treatment at 1100-1150 DEG C for 3h, and argon filling cooling; the wire cutting adopts high-speed reciprocating wire cutting, the pulse width is set to 30-40us, the pulse interval is 120-160us, the waveform is a rectangular pulse, and the cutting surface should be ensured to be smooth and smooth after wire cutting.

[0034] In the embodiment, the size precision of the large-diameter ratio cobalt-based high-temperature alloy double-component nozzle obtained after laser selective melting is ±0.1mm, the inner and outer surface cylindricity of the nozzle is ≤0.1mm, the coaxiality is ≤0.1mm, and the surface roughness Ra is 6.3um.

[0035] In the embodiment, the particle size distribution of the cobalt-based high-temperature alloy powder is D10 of 18-28um, D50 of 30-45um, D90 of 55-65um, the loose density of the powder is 5.35-5.55g / cm 3 , and the flowability of 50g cobalt-based high-temperature alloy powder is ≤45s.

[0036] Although the present application has been disclosed with the above preferred embodiments, it is not intended to limit the present application, and any person skilled in the art can make possible changes and modifications to the technical solutions of the present application by using the disclosed methods and technical contents without departing from the spirit and scope of the present application. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application, which does not deviate from the technical solutions of the present application, belongs to the protection scope of the technical solutions of the present application.

[0037] The contents not described in detail in the specification of the present application belong to the known technology of the person skilled in the art.

Claims

1. A method of laser powder bed fusion forming of a large aspect ratio cobalt- based superalloy bi-component nozzle, characterized in that, The application relates to a method for manufacturing a large-length-diameter-ratio cobalt-based high-temperature alloy double-element nozzle. The method comprises the following steps: a three-dimensional model corresponding to the large-length-diameter-ratio cobalt-based high-temperature alloy double-element nozzle is determined; wherein the length of the large-length-diameter-ratio cobalt-based high-temperature alloy double-element nozzle is 250mm-400mm, the diameter is Phi5mm-Phi10mm, and the circumferential hole diameter is Phi1.0mm-Phi5.0mm; a process allowance is designed for the three-dimensional model corresponding to the large-length-diameter-ratio cobalt-based high-temperature alloy double-element nozzle, and a manufacturing model is obtained; wherein the process allowance comprises a product shrinkage compensation allowance and a machining allowance; the product shrinkage compensation allowance is that a 0.12% shrinkage allowance is designed for the three-dimensional model corresponding to the large-length-diameter-ratio cobalt-based high-temperature alloy double-element nozzle; and the machining allowance is 0.5mm; different cobalt-based high-temperature alloy laser selective melting forming process parameters are adopted to simulate and analyze stress / strain distribution in the manufacturing process of the manufacturing model, and according to the stress / strain distribution result, a cobalt-based high-temperature alloy laser selective melting forming process parameter with the minimum deformation is selected as the final manufacturing process parameter; the cobalt-based high-temperature alloy laser selective melting forming process parameter comprises a layer thickness of 0.03mm, a laser scanning interval of 0.10mm, a laser power of 230-240W, a laser scanning speed of 860-880mm / s, a phase angle of 67 DEG and a root radius R of a nozzle and a base plate contact of 2mm; the manufacturing model is subjected to slicing treatment, and the final manufacturing process parameter is inputted to obtain laser scanning path data of each slice layer; the obtained laser scanning path data of each slice layer is inputted into a suitable laser selective melting forming equipment, a stainless steel base material is installed, an inert gas environment is replaced in a forming chamber, cobalt-based high-temperature alloy powder is adopted, and a double-element nozzle is formed; wherein the inert gas is argon; and the oxygen content in the manufacturing chamber is less than 500PPM during the forming process; after laser selective melting, loose powder on the inner and outer surfaces of the double-element nozzle is blown off, stress relief heat treatment is carried out, and the base plate and the double-element nozzle are subjected to wire cutting separation; wherein the loose powder on the inner and outer surfaces of the double-element nozzle is blown off by adopting 0.6Mpa-0.8Mpa compressed air and an ultrasonic vibration platform to clean the loose powder in the double-element nozzle and the surface loose powder obtained by laser selective melting; the stress relief heat treatment is carried out by adopting the following method: solid solution treatment at 1100 DEG C-1150 DEG C for 3h under vacuum and argon gas cooling; the cutting separation is carried out by adopting high-speed reciprocating wire spark cutting, the pulse width is set to 30-40mu s, the pulse interval is 120-160mu s, the waveform is a rectangular pulse, and the cutting surface needs to be ensured to be neat and smooth after the wire cutting is completed; the size precision of the large-length-diameter-ratio cobalt-based high-temperature alloy double-element nozzle obtained after laser selective melting is + / -0.1mm, the inner and outer surface cylindricity of the nozzle is less than or equal to 0.1mm, the coaxiality is less than or equal to 0.1mm, and the surface roughness Ra is 6.3mu m. The cobalt-based superalloy powder has a particle size distribution of D10 of 18-28 μm, D50 of 30-45 μm, and D90 of 55-65 μm, and a bulk density of 5.35-5.55 g / cm 3 , and the flowability of 50 g of the cobalt-based superalloy powder is ≤45 s.

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