Sandwich runner structure selective laser melting forming and post-processing method

Abstract

The invention relates to a selective laser melting forming and post-processing method for a complex interlayer runner structure, which ensures the dimensional accuracy of a product by performing segmented scaling on a model according to the shrinkage characteristic of additive manufacturing in the printing process, so that the runner size of the product meets the requirement. According to the use condition of the product, dot matrix lightweight filling is conducted on the solid reinforcing rib supporting part of the product, and high-performance self-supporting weight reduction of the product is achieved. The characteristics of good fluidity and low viscosity of sodium stearate are utilized, and a conventional runner wax filling mode is replaced by sodium stearate filling to carry out redundancy protection, so that the risk that the redundancy is formed by runner filling residues is remarkably reduced. And the integrated interlayer flow channel is finely and efficiently finished by adopting a circulating flow channel chemical finishing method, so that the surface quality of a product is ensured to meet the requirement.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing, and in particular relates to a method for selective laser melting forming and post-processing of a sandwich flow channel structure. Background Art

[0002] The nozzle with complex integrated sandwich flow channel structure is the main structural form that effectively ensures the normal service of the ramjet engine thrust chamber under high temperature and high pressure environment. It is mainly composed of three parts: the air inlet, the combustion chamber, and the propulsion nozzle. When the engine is working, the working environment of the nozzle throat section is a high temperature and high pressure environment, which is extremely harsh. The working temperature is as high as 1600K or above, and the high temperature gas flushing speed exceeds 1000m / s. The nozzle manufactured by the traditional manufacturing process is usually single-walled, made of high temperature alloy, with a coating on the wall, and poor temperature resistance. The complex sandwich flow channel structure can achieve efficient cooling of the ramjet engine nozzle. The traditional manufacturing process method cannot directly form a complex integrated sandwich flow channel structure, and is generally manufactured by the inner and outer wall brazing process. The above processing technology has the following problems: First, the performance stability is poor. The sandwich flow channel structure of the combustion chamber nozzle adopts the inner and outer wall brazing process, and the cooling channel is often blocked or bulged due to uneven flow of brazing material, which affects the product performance. In addition, the nozzle throat section adopts the process of brazing and then welding. Due to the deformation of each section after brazing, the docking accuracy and weld quality of each section are poor, which reduces the quality and stability of the engine. Second, the qualification rate is low. When assembling the inner and outer walls of the sandwich cooling assembly, the inner wall needs to be bulged to make the inner and outer walls fit together. However, due to the rebound of the material, the brazing gap between the inner and outer walls of the small end is large after bulging, resulting in poor brazing quality. During the subsequent hydraulic test assessment, problems such as pressure bulging will occur in the weaker areas of the brazing seam, resulting in product scrapping. Third, the processing cycle is long. Since the sandwich flow channel assembly cannot be formed as a whole using traditional processes, it needs to be divided into multiple sections. Each section is brazed separately and then welded into an overall structure. The structure and process flow are complex. The forming process involves more than a dozen processes such as forging, heat treatment, machining, bulging, brazing, and electron beam welding, resulting in a long production cycle. The entire production cycle takes nearly 5 months, which is not conducive to the rapid development of the engine. Summary of the invention

[0003] The present invention provides a method for laser selective melting forming and post-processing of a sandwich flow channel structure. According to the shrinkage characteristics of additive manufacturing during the printing process, the overall forming of the sandwich flow channel structure can be achieved through segmented scaling of the model, with fast forming speed and reliable quality.

[0004] The above-mentioned purpose of the present invention is mainly achieved through the following technical solutions:

[0005] A method for selective laser melting forming and post-processing of a sandwich flow channel structure comprises the following steps:

[0006] (1) Establish a three-dimensional model of the sandwich channel structure with a substrate and support, and perform dot filling on the rib support part (VI) of the model;

[0007] (2) According to the three-dimensional model of the sandwich flow channel structure obtained in step (1), the model is divided into three parts: the flange part, the part from the upper end face of the flange to the inner part of the product, and the part from the inner part of the product to the upper end face of the product. The three parts of the model are scaled respectively, and then conical solid supports and block mesh supports are added;

[0008] (3) performing laser selective melting forming according to the scaled three-dimensional model of the sandwich flow channel structure obtained in step (2) to obtain a sandwich flow channel structure with a substrate and a support;

[0009] (4) removing the inner cavity powder of the sandwich flow channel structure with the substrate and the support obtained in step (3), and pouring sodium stearate for protection;

[0010] (5) separating the substrate and the sandwich flow channel structure obtained in step (4), removing the conformal external support, and then performing a sodium stearate removal treatment;

[0011] (6) heat treating and surface finishing the sandwich flow channel structure obtained in step (5);

[0012] The sandwich flow channel structure includes an inner wall, an outer wall, a rib wall, an upper liquid collecting ring, a lower liquid collecting ring and a reinforcing rib support portion. The upper liquid collecting ring and the lower liquid collecting ring are respectively arranged at both ends of the outer wall. The rib wall is between the inner wall and the outer wall, and the rib wall is a through structure.

[0013] In step (1), the flange end of the three-dimensional model of the sandwich flow channel structure is placed close to the base plate.

[0014] In step (1), the cell size of the filling lattice is not less than 4 mm, the diameter of the formed rod is not less than 1 mm, and the relative density is not less than 5%.

[0015] Step (2) After the model is scaled, the transition parts between adjacent parts are rounded and smoothed, with the size of the rounded corners being R15-R20.

[0016] The parameters of the block grid support and conical solid support in step (2) are as follows: the filling size of the small block grid is 0.6*0.6mm, the rotation angle is 30°, the filling size of the large block grid is 3*3mm, the rotation angle is -20°, the diameter of the conical solid support is 0.5-0.7mm, and the minimum distance between vertebrae is 1.5-2mm.

[0017] In step (2), an OXYZ coordinate system is established, requiring the OXY plane to be parallel to the lower bottom surface, and the model scaling ratios are as follows: the scaling ratios of the flange part in the X-axis, Y-axis and Z-axis directions are 1.0035-1.0037, 1.0035-1.0037 and 1.0005, respectively; the scaling ratios of the flange upper end surface to the internal part of the product in the X-axis, Y-axis and Z-axis directions are 1.0037-1.0040, 1.0037-1.0040 and 1.0005, respectively; the scaling ratios of the product internal part to the upper end surface of the product in the X-axis, Y-axis and Z-axis directions are 1.0039-1.0043, 1.0039-1.0043 and 1.0005, respectively.

[0018] In step (3), the entity parameters of laser selective melting are: laser power of 115-150W, scanning speed of 500-650mm / s, line spacing of 0.09mm, and spot diameter of 100μm; the upper surface parameters are: laser power of 170-200W, scanning speed of 2300-2450mm / s, line spacing of 0.05mm, and spot diameter of 100μm; the lower surface parameters are: laser power of 170-200W, scanning speed of 2300-2450mm / s, line spacing of 0.05mm, and spot diameter of 100μm.

[0019] In step (4), the method for removing powder from the inner cavity is rotational vibration and ultrasonic cleaning, which is as follows: place the product on a rotational vibration platform, introduce 0.5-0.8MPa compressed air to remove internal powder, the vibration frequency is 3000-4000HZ, the rotation angle is 120°-180°, the rotation speed is 3° / s, the vibration time is 15-20h, and ultrasonic cleaning equipment is used to remove residual powder inside the component, the water temperature is 40-60°C, and the cleaning time is 15-25h.

[0020] The separation method in step (5) is as follows: high-speed reciprocating wire cutting is adopted by electric spark wire cutting method, the pulse waveform is rectangular, the pulse width is 25-40μs, the pulse interval is 160-210μs, and the current is 3-6A.

[0021] The sodium stearate removal treatment method in step (5) is as follows: immerse the sandwich flow channel structure in 110°C water for 3-5 hours, and then use 100°C steam to blow off the inner flow channel opening and outer surface of the product.

[0022] In step (6), the heat treatment and surface finishing methods are as follows: vacuum stabilized state heat treatment is adopted, the heat treatment temperature is 840-860°C, the time is 115-125min, argon gas or high-purity nitrogen is backfilled, and the cooling pressure is 1-2bar; the surface finishing method is chemical polishing, and the polishing liquid is pumped into the flow channel by a pump-pushing method. The polishing liquid is a mixed solution of hydrochloric acid, nitric acid, and hydrofluoric acid. The polishing liquid flows evenly in the sandwich flow channel structure at a pressure of 0.15-0.20MPa, and the polishing time is 35-40min.

[0023] The material of the sandwich channel structure is 06Cr19Ni10.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects:

[0025] (1) The present invention ensures the dimensional accuracy of the product by scaling the model in sections based on the shrinkage characteristics of additive manufacturing during the printing process, so that the product flow channel size meets the requirements.

[0026] (2) The present invention performs lattice lightweight filling on the solid reinforcement rib support parts of the product according to the product usage conditions, thereby achieving high-performance self-supporting weight reduction of the product.

[0027] (3) The present invention adopts sodium stearate filling to replace the conventional flow channel wax filling method to protect against excess materials, and utilizes the good fluidity and low viscosity of sodium stearate to significantly reduce the risk of excess materials formed by flow channel filling residues.

[0028] (4) The present invention preferably adopts a circulating flow channel chemical finishing method to polish the integrated sandwich flow channel, and the flow channel is finely and efficiently finished, ensuring that the product surface quality meets the requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a front view of the sandwich flow channel structure of the present invention;

[0030] Figure 2 It is a structural diagram of the sandwich flow channel structure of the present invention;

[0031] Figure 3 This is a diagram of the inner flow channel structure of the sandwich flow channel structure of the present invention. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0033] like Figure 1 The front view of the sandwich flow channel structure of the present invention is shown. Figure 2 The structure diagram of the sandwich flow channel structure of the present invention is shown. Figure 3The figure shows the inner flow channel structure diagram of the sandwich flow channel structure of the present invention. The sandwich flow channel structure includes inner wall I, outer wall II, rib wall III, upper liquid collecting ring IV, lower liquid collecting ring V and reinforcing rib support part VI. The upper liquid collecting ring IV and lower liquid collecting ring V are respectively arranged at both ends of the outer wall II. The rib wall III is between the inner wall I and the outer wall II, and together they constitute a through-type sandwich channel, and the minimum channel size is 5*5mm. The coolant enters the structure through the four inlets of the upper liquid collecting ring IV, flows in the cooling channel to cool the sandwich structure. The channel inside the component is an airflow channel, and the air flows in the inner channel.

[0034] The present invention provides a method for selective laser melting forming and post-processing of a sandwich flow channel structure, comprising the following steps:

[0035] (1) Establish and optimize the three-dimensional model of the component:

[0036] Use modeling software UG or Creo to establish a three-dimensional model of the component, comprehensively consider many applicable conditions of the component such as structural strength, hydraulic pressure, and airtightness, eliminate as many connection structures and welds in the component model as possible, and make adaptive modifications for additive manufacturing so that some structures can be self-supporting and formed, and obtain complex integrated sandwich flow channel components. Then export the three-dimensional model in STL format with an export accuracy better than 0.004mm.

[0037] (2) The three-dimensional model established in step (1) is placed in Magics software as required: In order to ensure the growth strength of the component on the substrate and the working strength of the structural parts during the printing process, as well as to ensure the integrity and consistent forming of the flow channel, the lower end face of the component flange is placed close to the substrate.

[0038] (3) In order to reduce the weight of the structural parts, the outer wall solid reinforcement rib support part VI is filled with a lattice. The cell size of the filled lattice is not less than 4 mm, the diameter of the formed rod is not less than 1 mm, and the relative density is not less than 5%.

[0039] (4) Segmented scaling of the product model. In step (2), an OXYZ coordinate system is established, requiring the OXY plane to be parallel to the bottom surface. The scaling ratios of the model are as follows: the scaling ratios of the flange part (①-② area) in the X-axis, Y-axis and Z-axis directions are 1.0035-1.0037, 1.0035-1.0037 and 1.0005, respectively; the scaling ratios of the flange upper end surface to the product interior (②-③ area) in the X-axis, Y-axis and Z-axis directions are 1.0037-1.0040, 1.0037-1.0040 and 1.0005, respectively; the scaling ratios of the product interior to the product upper end surface (③-④ area) in the X-axis, Y-axis and Z-axis directions are 1.0039-1.0043, 1.0039-1.0043 and 1.0005, respectively.

[0040] The segmented transition part is rounded by chamfering, and the rounded size is R15-R20. Block mesh support and conical solid support are added at the overhang surface (<50°) of the product. The filling size of the small block mesh is 0.6*0.6mm, the rotation angle is 30°, the filling size of the large block mesh is 3*3mm, the rotation angle is -20°, the diameter of the conical solid support is 0.5-0.7mm, and the minimum distance between the vertebrae is 1.5-2mm.

[0041] (5) The physical parameters of laser selective melting are: laser power 115-150 W, scanning speed 500-650 mm / s, line spacing 0.09 mm, and spot diameter 100 μm; the upper surface parameters are: laser power 170-200 W, scanning speed 2300-2450 mm / s, line spacing 0.05 mm, and spot diameter 100 μm; the lower surface parameters are: laser power 170-200 W, scanning speed 2300-2450 mm / s, line spacing 0.05 mm, and spot diameter 100 μm.

[0042] (6) Place the product on a rotating vibration platform and pass 0.5-0.8MPa compressed air into the flow channel to remove the powder inside the component. The vibration frequency is 3000-4000HZ, the rotation angle is 120°-180°, the rotation speed is 3° / s, and the vibration time is 15-20h. Use ultrasonic cleaning equipment to remove the residual powder inside the component. The water temperature is 40-60℃ and the cleaning time is 15-25h. Sodium stearate is poured into the component. It has good fluidity and low viscosity, which is easy to remove and prevents excess matter from entering the flow channel.

[0043] (7) Use the electric spark wire cutting method for high-speed reciprocating wire cutting, pulse waveform: rectangular, pulse width: 25-40μs, pulse interval: 160-210μs, current: 3-6A. Use a sharp scraper to manually chisel to remove large supports, and then use a pneumatic grinding gun to fine-tune the surface of the structural parts. The method for removing sodium stearate is: soak the product in 110℃ high-temperature water for 3-5h, and then use 100℃ high-temperature steam to blow off the inner flow channel and outer surface of the product to ensure that the product is dry and the cleanliness meets the requirements.

[0044] (8) The structural material is 06Cr19Ni10, and vacuum stabilized heat treatment is adopted. The specific system is: temperature: 840-860℃, time: 115-125min, backfilling argon or high-purity nitrogen, cooling pressure is 1-2bar. The surface finishing method is chemical polishing, and the polishing liquid is pumped into the flow channel by a pump-pushing method. The polishing liquid is a mixed solution of hydrochloric acid, nitric acid, and hydrofluoric acid. The polishing liquid flows evenly in the complex integrated sandwich flow channel structure component at a rated pressure of 0.15-0.20MPa, and the polishing time is 35-40min.

[0045] The above description is only the best specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

[0046] The contents not described in detail in the specification of the present invention belong to the common knowledge of the professionals in this field.

Claims

1. A method for selective laser melting forming and post-processing of a sandwich flow channel structure, characterized in that: The following steps are involved: (1) Establish a three-dimensional model of the sandwich channel structure with a substrate and support, and perform dot filling on the rib support part (VI) of the model; (2) According to the three-dimensional model of the sandwich flow channel structure obtained in step (1), the model is divided into three parts: the flange part, the part from the upper end face of the flange to the inner part of the product, and the part from the inner part of the product to the upper end face of the product. The three parts of the model are scaled respectively, and then conical solid supports and block mesh supports are added; (3) performing laser selective melting forming according to the scaled three-dimensional model of the sandwich flow channel structure obtained in step (2) to obtain a sandwich flow channel structure with a substrate and a support; (4) removing the inner cavity powder of the sandwich flow channel structure with the substrate and the support obtained in step (3), and pouring sodium stearate for protection; (5) separating the substrate and the sandwich flow channel structure obtained in step (4), removing the conformal external support, and then performing a sodium stearate removal treatment; (6) heat treating and surface finishing the sandwich flow channel structure obtained in step (5); The sandwich flow channel structure comprises an inner wall (I), an outer wall (II), a rib wall (III), an upper liquid collecting ring (IV), a lower liquid collecting ring (V) and a reinforcing rib supporting portion (VI); an upper liquid collecting ring (IV) and a lower liquid collecting ring (V) are respectively arranged at both ends of the outer wall (II); the rib wall (III) is located between the inner wall (I) and the outer wall (II); and the rib wall (III) is a through structure.

2. The method for selective laser melting forming and post-processing of a sandwich flow channel structure according to claim 1, characterized in that: In the step (1), the flange end of the three-dimensional model of the sandwich flow channel structure is placed close to the base plate.

3. The method for selective laser melting forming and post-processing of a sandwich channel structure according to claim 1, characterized in that: In the step (1), the size of the filling lattice cell is not less than 4 mm, the diameter of the formed rod is not less than 1 mm, and the relative density is not less than 5%.

4. The method for selective laser melting forming and post-processing of a sandwich channel structure according to claim 1, characterized in that: After the model is scaled in step (2), the transition parts between adjacent parts are rounded and smoothed, and the size of the rounding is R15-R20.

5. The method for selective laser melting forming and post-processing of a sandwich flow channel structure according to claim 1, characterized in that: The parameters of the block grid support and conical solid support in step (2) are as follows: the filling size of the small block grid is 0.6*0.6mm, the rotation angle is 30°, the filling size of the large block grid is 3*3mm, the rotation angle is -20°, the diameter of the conical solid support is 0.5-0.7mm, and the minimum distance between vertebrae is 1.5-2mm.

6. The method for selective laser melting forming and post-processing of a sandwich flow channel structure according to claim 1, characterized in that: In step (2), an OXYZ coordinate system is established, requiring the OXY plane to be parallel to the bottom surface. The scaling ratio of the model is as follows: the scaling ratios of the flange part in the X-axis, Y-axis and Z-axis directions are respectively: 1.0035-1.0037, 1.0035-1.0037 and 1.0005; the scaling ratios of the upper end face of the flange to the inner part of the product in the X-axis, Y-axis and Z-axis directions are: 1.0037-1.0040, 1.0037-1.0040 and 1.0005; the scaling ratios of the product from the inside to the upper end surface in the X-axis, Y-axis and Z-axis directions are: 1.0039-1.0043, 1.0039-1.0043 and 1.0005.

7. The method for selective laser melting forming and post-processing of a sandwich channel structure according to claim 1, characterized in that: In the step (3), the entity parameters of the laser selective melting forming are: laser power of 115-150W, scanning speed of 500-650mm / s, line spacing of 0.09mm, and spot diameter of 100μm; the upper surface parameters are: laser power of 170-200W, scanning speed of 2300-2450mm / s, line spacing of 0.05mm, and spot diameter of 100μm; the lower surface parameters are: laser power of 170-200W, scanning speed of 2300-2450mm / s, line spacing of 0.05mm, and spot diameter of 100μm.

8. The method for selective laser melting forming and post-processing of a sandwich channel structure according to claim 1, characterized in that: In the step (4), the method for removing the powder in the inner cavity is rotational vibration and ultrasonic cleaning, which is as follows: place the product on a rotational vibration platform, introduce 0.5-0.8MPa compressed air to remove the internal powder, the vibration frequency is 3000-4000HZ, the rotation angle is 120°-180°, the rotation speed is 3° / s, the vibration time is 15-20h, and the residual powder inside the component is removed by ultrasonic cleaning equipment, the water temperature is 40-60°C, and the cleaning time is 15-25h.

9. The method for selective laser melting forming and post-processing of a sandwich channel structure according to claim 1, characterized in that: The separation method in step (5) is as follows: high-speed reciprocating wire cutting is performed using an electric spark wire cutting method, the pulse waveform is rectangular, the pulse width is 25-40 μs, the pulse interval is 160-210 μs, and the current is 3-6A.

10. The method for selective laser melting forming and post-processing of a sandwich channel structure according to claim 1, characterized in that: The sodium stearate removal treatment method in step (5) is as follows: immerse the sandwich flow channel structure in 110°C water for 3-5 hours, and then use 100°C steam to blow off the inner flow channel opening and outer surface of the product.

11. The method for selective laser melting forming and post-processing of a sandwich channel structure according to claim 1, characterized in that: In the step (6), the heat treatment and surface finishing methods are as follows: vacuum stabilized heat treatment is adopted, the heat treatment temperature is 840-860°C, the time is 115-125min, argon gas or high-purity nitrogen is backfilled, and the cooling pressure is 1-2bar; the surface finishing method is chemical polishing, and the polishing liquid is pumped into the flow channel by a pump-pushing method. The polishing liquid is a mixed solution of hydrochloric acid, nitric acid, and hydrofluoric acid. The polishing liquid flows evenly in the sandwich flow channel structure at a pressure of 0.15-0.20MPa, and the polishing time is 35-40min.

12. The method for selective laser melting forming and post-processing of a sandwich channel structure according to claim 1, characterized in that: The sandwich channel structural component is made of 06Cr19Ni10.

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