CN103464690A - Manufacturing method of ceramic mold of monocrystal turbine blade - Google Patents

Abstract

The invention discloses a method for manufacturing a single-crystal turbine blade ceramic mold. According to the grain orientation requirements of the single-crystal turbine blade, an integrated ceramic mold with a specific spiral crystal selector is designed and manufactured. When manufacturing single crystal blades by directional solidification, the thickness of the shell at the sudden change in section (such as the junction of the blade body and the edge plate) increases, the heat transfer capacity decreases, and it is easy to cause crystal defects such as miscellaneous crystals. , through topology optimization, design heat transfer channels, improve the heat transfer capacity of the mold, and then increase the temperature gradient at the front of the solid-liquid interface during directional solidification, so that the entire blade can obtain a good single crystal structure.

Description

A kind of manufacturing method of single crystal turbine blade ceramic mold

technical field

The invention belongs to the field of rapid casting, and relates to a method for manufacturing a single-crystal turbine blade ceramic mold.

Background technique

The single crystal blade is a blade developed based on directional solidification technology that completely eliminates the grain boundary texture along the direction of the blade body. It has excellent high temperature creep resistance, thermal mechanical fatigue resistance, oxidation corrosion resistance and high temperature bearing capacity. In order to obtain high-quality metal single crystals, a single crystal nucleus must first be formed in the metal melt. At present, in the manufacture of single crystal turbine blades, spiral crystal selectors are mainly used to obtain single crystal nuclei. The spiral crystal selector is a cavity set at the lower part of the casting body, which is composed of a crystal raising segment and a spiral crystal selecting segment. In the past, when manufacturing single crystal blades by investment casting, in order to obtain a complete casting prototype, it was necessary to assemble the wax pattern of the spiral crystal selector to the wax pattern of the blade, which was time-consuming and difficult to guarantee the accuracy. Therefore, it is particularly important to develop an integrated manufacturing method for a single crystal turbine blade resin model with a spiral crystal selector, which can well solve the shortcomings of low assembly accuracy and long time-consuming in the production of investment casting wax models in the past.

In the traditional investment casting method, the manufacturing of the shell mainly adopts the method of multiple coating and hanging, the shape of the produced shell is uncontrollable, and it is easy to cause the thick shell at the sudden change of section (the junction of the blade body and the edge plate) . In turn, the heat transfer capacity of this place is reduced, resulting in crystal defects such as miscellaneous crystals. In the past, in order to improve the thermal conductivity of the ceramic shell, technologies such as coating the graphite layer on the tenon of the blade shell and pasting graphite heat conductors at the corners of the thick section were used, which can better improve the thermal conductivity of the ceramic shell, but increase the shape. Difficulty and cost of shell manufacture. Therefore, the use of light-curing molding technology to manufacture resin mold shells with topological heat transfer channels, and then to manufacture molds with topological heat transfer channels, can improve the mold manufacturing without increasing the difficulty and cost of casting molds. The heat transfer capacity at the sudden change in the cross-section of the mold.

Contents of the invention

The problem to be solved by the present invention is to provide a method for manufacturing single crystal turbine blade ceramic molds, which solves the problems of low assembly precision of the spiral crystal selector and difficult control of grain shape in the manufacture of traditional single crystal turbine blade molds, and improves the efficiency of single crystal turbine blades. Quality and precision in blade manufacture.

The present invention is achieved through the following technical solutions:

A method for removing a monolithic ceramic casting resin mold, comprising the steps of:

1) According to the requirements of the grain orientation of the single crystal turbine blade, use the foundry finite element software to design a matching spiral crystal selector, including the number of turns of the spiral crystal selection section, the distance between adjacent spiral sections and the size of the crystal lifter;

2) Design the initial casting mold based on the single crystal hollow turbine blade with a spiral crystal selector, and import it into the casting finite element software for heat transfer and stress analysis; The shape of the outer wall of the mold shell is used to reduce the stress; according to the distribution of thermal stress at each time, the wall thickness that meets the thermal intensity and the minimum stress is selected, and the wall thickness is taken as the uniform wall thickness of the initial mold after stress relief, and the secondary mold;

3) Place the designed secondary mold in the simulation environment of directional solidification for heat transfer analysis, and obtain the heat transfer law and temperature gradient distribution of the secondary mold. For the sudden change of the section, the mold strength is used as the initial boundary condition , through topology optimization, design the heat transfer channel, improve the heat transfer capacity at the sudden change in the cross section, and form a tertiary casting mold;

4) Then repeat the heat transfer analysis, stress analysis and directional solidification simulation analysis for the three casting molds, and modify them until the temperature gradient requirements of the compound directional solidification at the variable cross-section, and can withstand the stress in the process of directional crystal growth, to obtain the shape casting type;

5) Manufacture the resin prototype mold through the light curing rapid prototyping technology of the designed mold, and use the method of gel injection molding to manufacture the single crystal turbine blade ceramic mold.

The turbine blade resin model with spiral crystal selector and the initial mold are designed and constructed in UG software.

The integrated manufacturing of the resin model of the turbine blade with the spiral crystal selector, the designed spiral crystal selector CAD model is assembled on the blade CAD model, and the three-dimensional model of the part is shelled by using the modeling software, and the solid part is It is hollowed out, and the thickness of the shell is 0.6-3mm, and then the resin prototype of the turbine blade with the spiral crystal selector is produced by using the light-curing rapid prototyping equipment.

The form of stress reduction in step 2) is to passivate the sharp part of the outer wall of the shell until the stress concentration is eliminated or reduced.

The secondary mold is placed in the simulation environment of directional crystal growth provided by ProCAST software for radiation heat transfer analysis, and the following settings are set when the preheating model is established in the ProCAST software:

5.1) Set the heat transfer coefficient of castings and shells to 0;

5.2) Set the heat transfer boundary condition on the surface of the formwork, set VIEW FACTOR to ON and set the radiation rate;

5.3) Set the casting to EMPTY, and set the casting status to FULL;

After completing the preheating calculation through the preheating model, use the temperature distribution results of the mold shell to establish a calculation model for radiation heat transfer analysis, including the following settings:

5.4) Extract the temperature distribution state of the formwork in the preheating calculation;

5.5) Change the zero heat transfer coefficient of castings and mold shells;

5.6) Remove the heat transfer boundary condition on the inner surface of the mold shell, and set the casting state to FULL;

Carry out radiation heat transfer analysis on the calculation model of radiation heat transfer analysis. During the analysis, the alloy material parameters of the castings are calculated using the Lever model, and the VIEW FACTOR is set to ON. The operating parameters are set in the Radiation module in the radiation heat transfer calculation. , corresponding to the radiation button box and the formwork;

After the radiation heat transfer analysis is completed, the temperature distribution and heat transfer law of the mold shell and castings are obtained, that is, the temperature field distribution map; the temperature gradient is calculated according to the temperature distribution and the model, and the temperature gradient distribution map is obtained; combined with the thermal stress field distribution , Temperature field distribution and temperature gradient distribution, conduct comprehensive analysis to guide mold design.

The moving speed of the radiation button box is set to the solidification speed of the molten metal used for castings.

The design of the initial ceramic mold uses finite element software to conduct heat transfer and grain structure analysis during the directional solidification process. The ceramic mold shell at the sudden cross-section is thick and the heat transfer capacity is reduced, which is likely to cause crystal defects. The mold strength As the initial boundary condition, through topology optimization, the mold structure is improved, the heat transfer channel is designed, and the heat transfer capacity is improved.

The resin prototype mold manufactured by the light-curing rapid prototyping technology is:

The design of the light-curing resin mold is completed in UG software. Based on the finalized casting mold, the pouring position is determined according to the function and shape of the component, and the pouring riser is designed; and the casting fillet R0.5~1 is added according to GB/T6414-1999; The cured resin mold is added with a pouring shell, the shell is 1-2mm thick, and reinforcing ribs are added to the shell;

After the design of the light-curing resin mold is completed, it is exported in STL form, and then the STL file is imported into the Magics software to extract the shell, add supports, and export the SLC file; load the SLC file into the RPbuild software of the light-curing molding machine, and control the automatic curing of the light-curing molding machine. Preparation of resin parts;

After the preparation is completed, remove the auxiliary support of the resin part, and clean the resin prototype with alcohol for 2 to 3 times to ensure that the residual liquid resin is completely cleaned up.

The gel injection molding adopts the following method to prepare ceramic slurry:

1) Calculate the volume of deionized water based on the volume of the light-curing resin mold and the solid phase content of the ceramic powder particles, then add organic monomers, crosslinking agents and dispersants in sequence, stir to dissolve, and adjust the pH of the solution with concentrated ammonia water 10 to 11 to obtain a premix solution with an organic concentration of 20%;

2) Add the ceramic powder to the premix solution in batches, add 2-3 times the mass of balls, and ball ink for about 1 hour to obtain a ceramic slurry with a viscosity of less than 1Pa·S and a solid phase volume fraction of 58-63vol%;

The ceramic powder mainly includes coarse-grained alumina powder with a particle size of 40 μm, fine-grained alumina powder with a particle size of 2-5 μm, and a magnesium oxide mineralizer.

The method for preparing the single crystal turbine blade ceramic mold by the gel injection molding comprises:

1) Add the catalyst and the initiator to the ceramic slurry in turn, and make it quickly and uniformly dispersed, then place the resin prototype mold in a vibrating grouting machine with a vibration frequency of 30Hz-60Hz, and inject the ceramic slurry to obtain a ceramic green body; Then freeze-dry under vacuum, so that the moisture in the ceramic biscuit is directly transformed from solid state to gaseous state;

2) Then remove the resin from the ceramic green body, pre-sinter after removing the resin, the pre-sintering temperature is <1250°C; there is a certain amount of ashes inside the pre-sintered ceramic mold, and the residual ash in the ceramic shell is cleaned with compressed air. Cleaning, the compressed air pressure is less than 2Mpa;

3) Finally, final sintering is carried out at a sintering temperature of 1350°C to 1550°C to obtain a ceramic mold.

Compared with the prior art, the present invention has the following beneficial technical effects:

The manufacturing method of the single-crystal turbine blade ceramic casting mold provided by the present invention designs and manufactures an integrated ceramic casting mold with a specific spiral crystal selector according to the grain orientation requirements of the single-crystal turbine blade. When manufacturing single crystal blades by directional solidification, the thickness of the shell at the sudden change in section (such as the junction of the blade body and the edge plate) increases, the heat transfer capacity decreases, and it is easy to cause crystal defects such as miscellaneous crystals. , through topology optimization, design heat transfer channels, improve the heat transfer capacity of the mold, and then increase the temperature gradient at the front of the solid-liquid interface during directional solidification, so that the entire blade can obtain a good single crystal structure.

The manufacturing method of the single crystal turbine blade ceramic mold provided by the present invention adopts the integrated design of CAD-CAE technology, so as to achieve the integration of the design; the modification of the three-dimensional model data can be guided by the finite element calculation results, for example: single During the finite element calculation of the directional solidification of the crystal turbine blade, it was found that the heat transfer capacity of the sudden change in the cross section of the casting mold is low, which is easy to cause grain defects. The heat transfer channel can be designed to modify the model to improve the heat transfer capacity of the model.

The manufacturing method of the single crystal turbine blade ceramic mold provided by the present invention also solves the problem of complex and uncontrollable heat transfer in the traditional mold during directional solidification, for example: the heat transfer performance of the sudden change in the section during casting is reduced, resulting in easy Crystal defects such as miscellaneous crystals appear.

The manufacturing method of the single crystal turbine blade ceramic casting mold provided by the present invention also avoids the problem of uncontrollable shape of the mold shell during traditional mold shell manufacturing, for example: it is impossible to set heat transfer channels in places where heat transfer needs to be enhanced, and it is impossible to place heat transfer channels where necessary Reinforcing ribs are arranged at places where the strength of the mold shell is strengthened, and the method of the invention can improve the adaptability of the mold according to the analysis and experiment results.

In the rapid casting process based on light-curing molding and the ceramic molding process of gel injection molding, the method of the invention solves the problem of low assembly accuracy existing in the manufacture of single crystal turbine blades by the traditional investment casting method. For example: in the manufacture of wax patterns, there is a deviation in the assembly of the spiral crystal selector wax pattern and the blade wax pattern.

The manufacturing method of the single-crystal turbine blade ceramic casting mold provided by the invention shortens the design and manufacturing cycle of the casting mold, improves the performance of the casting mold, and greatly reduces the production cost.

Description of drawings

Figure 1 is a schematic diagram of the design process of a single crystal turbine blade with a spiral crystal selector (from left to right: design of a spiral crystal selector, schematic diagram of a single crystal turbine blade, schematic diagram of a model after assembly)

Figure 2 is a schematic diagram of a blade as a casting;

Fig. 3 is the schematic diagram of the pouring system of casting;

Fig. 4 is the three-dimensional design schematic diagram of mold;

Fig. 5 shows the time-stress variation of shell thermal stress with thickness, the abscissa is time, and the ordinate is stress;

Fig. 6 is the time-thermal stress variation of shell thermal stress with thickness, the abscissa is time, and the ordinate is thermal stress;

Figure 7 is an analysis diagram of the thermophysical parameters of the casting (Ni-based superalloy K4169), in which the abscissa in each figure is the temperature, and the ordinate is the solid phase ratio, thermal conductivity, density and enthalpy;

Figure 8 is the temperature field distribution map at the variable section and the schematic diagram of the high temperature area (from left to right: the cloud map of the temperature field at the variable section, the back schematic diagram of the high temperature area, and the front schematic diagram of the high temperature area);

Fig. 9 is a schematic diagram of the position of the variable section;

Fig. 10 is a schematic diagram of heat transfer channel distribution;

Figure 11. The cloud diagram of the temperature field distribution at the variable section after the final optimization.

Detailed ways

The present invention will be further described in detail below in conjunction with specific embodiments, which are explanations of the present invention rather than limitations.

A method for manufacturing a single crystal turbine blade ceramic mold, comprising the following steps:

1) According to the requirements of the grain orientation of the single crystal turbine blade, combined with the calculation and experiment of casting finite element software, design the spiral crystal selector, including the number of turns of the spiral crystal selection section, the distance between adjacent spiral sections and the size of the crystal lifter ;

2) Design the initial casting mold based on the single crystal hollow turbine blade with a spiral crystal selector, and import it into the casting finite element software for heat transfer and stress analysis; The shape of the outer wall of the mold shell is used to reduce the stress; according to the distribution of thermal stress at each time, the wall thickness that meets the thermal intensity and the minimum stress is selected, and the wall thickness is taken as the uniform wall thickness of the initial mold after stress relief, and the secondary mold;

3) Place the designed secondary casting mold in the simulation environment of directional solidification for heat transfer analysis, and obtain the heat transfer law and temperature gradient distribution of the secondary casting mold. The ceramic mold shell is thick, the heat transfer capacity is reduced, and it is easy to cause crystal defects such as miscellaneous crystals. Taking the mold strength as the initial boundary condition, through topology optimization, the heat transfer channel is designed to improve the heat transfer capacity at the sudden change in the cross-section, forming three times mold;

4) Then repeat the heat transfer analysis, stress analysis and solidification structure analysis of the three casting molds, and modify them until the temperature gradient requirements of the compound directional solidification at the variable cross-section, and can withstand the stress in the process of directional crystal growth, to obtain the stereotyped casting mold ;

5) Manufacture the resin prototype mold through the light-cured rapid prototyping technology of the designed mold, and use the method of gel injection molding to manufacture the final mold.

Specifically, for the design of the resin model of a turbine blade with a spiral crystal selector, the design process of a certain type of single crystal turbine blade resin model is given below:

According to the requirements of the grain orientation of single crystal turbine blades, combined with the calculation and experiment of casting finite element software, the spiral crystal selector is designed, including the number of turns of the spiral crystal selection section, the distance between adjacent spiral sections and the size of the crystal lifter. 3D modeling software modeling.

According to the national standard GB/T6414-1999 "Casting Dimensional Tolerance", the transition section is designed, and the three-dimensional model of the spiral crystal selector is assembled on the turbine blade to be manufactured.

Export the STL file, and use the light curing molding process to make a resin model of the turbine blade with a spiral crystal selector as a prototype for casting. The design process of a certain type of single crystal turbine blade resin model is shown in Figure 1.

Specifically, the mold design process of a certain type of turbine blade with topological heat transfer channels:

According to the three-dimensional model of the turbine blade shown in Figure 2, the height of the blade is about 192.5mm, the connection to the falcon root is about 80mm, and the widest part of the falcon root is about 166mm. Combined with the top pouring pouring position design, considering the principle of setting the thin-walled airfoil at a position far away from the pouring riser, the pouring system as shown in Figure 3 is designed. The choice of the top injection type is based on the following considerations: the shape of the hollow turbine blade of the gas turbine is complex, the wall is thin and uneven, and the unreasonable gating system causes more defects in the blade. It is not easy to completely fill the thin-walled structure with the bottom pouring gating system, so the top pouring pouring position is selected.

In addition, the airfoil is set away from the pouring riser because of the following considerations: in the process of directional solidification, the casting mold is firstly preheated, and then the vacuum smelted molten metal completely fills the casting mold, and then moves to the directional solidification furnace The heating zone, adiabatic zone and cooling zone are used for directional crystal growth. Setting the position of the pouring riser in this way makes the quality of the manufactured blades higher.

According to the foundry engineer's manual, the upper end diameter of the sprue cup is designed to be 140mm, the lower end diameter is 80mm, and the height of the sprue cup is 50mm. The area of the inner runner is checked by the blockage area method, that is, the Osann formula, and the size of the pouring riser is checked by the modulus method. The above-mentioned size meets the actual pouring requirements.

Design the casting mold according to Figure 3, and see Figure 4 for the three-dimensional drawing of the casting mold. Design the initial mold in 3D software (such as UG software), and the wall thickness of the mold at this time is uniform. For example, several shells with uniform wall thickness of 6mm, 9mm, 12mm and 15mm are selected for thermal stress calculation. And the thermal stress calculation is carried out in the stress analysis module of ProCAST software. Note that the thermal stress calculation here is the calculation of the ordinary thermal field and stress field, not the calculation under the condition of directional solidification, because the filling of the molten metal has been completed before entering the directional solidification furnace.

Figure 5 and Figure 6 are the thermal stress analysis at the riser of different thickness shells. It can be seen from the figure that when the thickness of the shell is reduced from 15mm to 9mm, the thermal stress at any moment will decrease with the decrease of thickness , and when the thickness of the shell is 6mm, the thermal stress of the shell increases significantly, even higher than that of the shell with a thickness of 15mm.

Among them, Figure 5 is a diagram of the change of thermal stress over time. The square represents the thermal stress change diagram with a thickness of 6mm, which is the uppermost curve; the dot represents the thermal stress change diagram with a thickness of 9mm, which is the lower curve; the upper triangle represents the thickness. It is the thermal stress change diagram of 12mm, which is the second curve from the bottom; the lower triangle represents the thermal stress change diagram with a thickness of 15mm, which is the third curve from the bottom, indicating that the thermal stress of the shell with a thickness of 9mm is the smallest . It can be seen from Figure 6 that at each moment, the thermal stress of the shell with a thickness of 9 mm is the minimum.

Then the initial mold is placed in a directional crystal growth simulation environment (such as ProCAST software) for thermal stress and radiation heat transfer analysis. Then import the initial casting mold into casting software (such as ProCAST software) for heat transfer and stress analysis, check the thermal stress distribution at each moment, and determine an optimal shell wall thickness that meets the thermal strength design.

To complete the radiation heat transfer analysis, the preheating calculation needs to be completed in the ProCAST software, and the establishment of the preheating model needs to pay attention to:

1) Set the heat transfer coefficient of the casting and the shell to 0;

2) Set the heat transfer boundary condition on the surface of the formwork, set VIEW FACTOR to ON and set the emissivity;

3) Set casting to EMPTY.

After completing the preheating calculation, use the temperature distribution results of the mold shell to establish a calculation model for radiation heat transfer analysis. In radiation heat transfer, it is necessary to pay attention to:

1) Extract the temperature distribution state of the formwork in the preheating calculation;

2) Change the zero heat transfer coefficient of castings and mold shells;

3) Remove the heat transfer boundary conditions on the inner surface of the mold shell. Since the filling of the molten metal is completed in the vacuum melting furnace during the directional solidification process, the calculation here only needs to complete the heat transfer calculation, so the casting state is set to FULL.

The main control points simulated in the heat transfer calculation are:

1) High temperature alloy material parameters. Generally, the composition of superalloys used in hollow turbine blades is very complex, and there is no ready-made material parameter map to check. But it can be calculated according to the calculation model. ProCAST software has a material parameter database and a calculation model for calculation, which can complete the calculation of superalloy material parameters. The calculation of superalloy material parameters adopts the Lever model.

2) Boundary conditions. In the first step of preheating calculation and the second step of radiation heat transfer calculation, VIEWFACTOR must be set to ON state.

3) The operating parameters are set in the Radiation module (RUN PARAMETER) in the radiation heat transfer calculation. Pay attention to the correspondence between the radiation box and the formwork.

Specifically, the thermal field analysis is performed on a shell with a uniform wall thickness of 9mm. The thermal physical parameters of the shell used in the thermal field analysis are: thermal diffusivity 1.513±0.002mm2/s, specific heat 0.784±0.017J/(g K), thermal conductivity 2.3580.004W/(m K) . The above thermal physical parameters were measured by LFA447 flash thermal conductivity meter. The thermal physical parameters of the blade used in the thermal field analysis can be calculated from the ProCAST software material database, as shown in Figure 7.

The above thermal physical property parameters were input into ProCAST software for thermal field calculation. The initial condition is that the liquid metal temperature of the blade is 1600°C, and the shell temperature is 1550°C by radiation heating. The boundary conditions are the 35°C water-cooling plate boundary at the bottom of the blade, and the 35°C condensation ring boundary at the solidification interface.

In the process of stress calculation, check the area of stress concentration. The existence of stress concentration will cause defects such as hot cracks in the mold shell or cracks in the impact of molten metal during the directional solidification process of the complex structure of the superalloy. In order to avoid these defects and problems The emergence of the need to reduce stress on the outer wall of the shell. The form of stress relief is mainly the sharp part of the outer wall of the passivation shell.

It should be noted that in the process of directional solidification, the mold is heated and dissipated by radiation, and the radiation buckle box should be added in the calculation process of ProCAST. The movement rate of the buckle box is generally set to the solidification rate of the molten metal.

After completing all the above calculations, the temperature distribution and heat transfer law of the mold shell and blade castings will be obtained, that is, the temperature field distribution map; the temperature gradient calculation (ProCAST temperature parameter calculation method) is performed according to the temperature distribution and the model, that is, the temperature gradient distribution map. Combined with the thermal stress field distribution, temperature field distribution and temperature gradient distribution of stress calculation, a comprehensive analysis is carried out to guide the mold design.

Figure 8 shows the temperature field distribution at the variable section (the junction of the blade body and the edge plate) during the primary design of the mold. It can be seen that the heat transfer capacity is reduced due to the sudden thickening of the shell at the variable section, and unevenness is formed inside the blade. The temperature field, the main high temperature area is located around the exhaust side (as shown in Figure 8). The uneven temperature field distribution is likely to cause defects such as miscellaneous crystals at the root of the blade, thereby reducing the performance of the overall blade (the location of the variable cross-section is shown in Figure 9).

The temperature distribution of the mold is not only related to the physical parameters of the mold and the casting, but also mainly depends on the shape of the mold. Therefore, in order to obtain a relatively average temperature field distribution at the variable section, it is necessary to perform topology optimization on the mold structure at this place.

According to the distribution law of the temperature field of the initial mold, the structural topology optimization is carried out for the high temperature region. By designing the heat transfer channel perpendicular to the surface of the shell, the purpose of improving the heat dissipation capacity of the shell is achieved. The specific implementation method: according to the temperature field distribution cloud map, determine the location of the high temperature area, design the heat transfer channel, and the main control parameters of the heat transfer channel are: : channel aperture R, channel depth D and inter-channel spacing G. In the slow heat dissipation area, increase the channel aperture and depth, reduce the distance between channels, and in the fast heat dissipation area, reduce the channel aperture and depth, increase the distance between channels, or even not design heat dissipation channels. Then repeat the calculation and modify the parameters of the heat transfer channel until the temperature distribution in the entire section is uniform, modify the secondary design, and complete the tertiary design. The above design must be completed under the condition of meeting the mold strength requirements; 2. The minimum value of the mold thickness is the mold thickness calculated according to the stress.

The specific design method of the heat transfer channel is as follows:

Take out the cloud diagram of the temperature field at the variable section for analysis, as shown in Figure 8. It was observed that the topological shape of the cross-section of the blade was oblate and concave on the long side. During the heat dissipation process, the heat dissipation of the accessories located on the exhaust side is relatively slow. In order to keep the temperature field in the same cross-section mold consistent, that is, there is no temperature gradient in the circumferential and radial directions of the shell, the distribution results calculated according to the temperature field Design topological heat transfer channels. Design the heat transfer channel for each high-temperature area separately, and check the temperature field distribution until the design of the heat transfer channel is completed at the entire cross-section, and finally form the secondary design.

As shown in Figure 8, the high-temperature area is located in the black frame, where the heat dissipation is slow, and the design of the heat transfer channel is required. The heat transfer channel is arranged according to the temperature distribution measurement calculated by the software, and the aperture R of the heat transfer channel is designed. Depth D and spacing G, improve the heat dissipation capability of this area. The designed heat transfer channel distribution is shown in Figure 10. And import the modified mold into Procast software for heat transfer analysis and optimization calculation.

The above design method is the topological optimization design method of the shell heat transfer channel in a certain high-temperature area at the variable cross-section. If the entire variable cross-section is to meet the requirement of uniform temperature field distribution, the design of each area must be completed according to the above-mentioned design and analysis methods. After the design is completed, import the 3D data of the casting mold into Procast software for radiation heat transfer calculation. If the ideal temperature distribution result is not obtained, a heat transfer channel is needed, and the above steps are repeated until the requirement of uniform temperature distribution is met.

After obtaining the optimized mold thickness, perform stress and general heat transfer calculations in the ProCAST software again to check the strength of the mold shell.

Tertiary mold design:

After the secondary design is completed, the mold with heat transfer channels is placed in ProCAST software for radiation heat transfer calculations. Thermophysical parameters, initial conditions, boundary conditions, etc. are not changed. Then check the temperature field, analyze the temperature gradient, further modify the parameters of the heat transfer channel, and carry out three designs. Figure 11 shows the final optimized cross-section temperature field distribution. The entire cross-section temperature field is evenly distributed, and there is no obvious high-temperature area inside the blade. .

Then repeat the stress calculation and heat transfer calculation, and modify the design until the temperature field at the entire variable section is evenly distributed and can withstand the stress in the process of directional crystal growth, and determine the three-dimensional design of the mold, which is the final design of the shell.

After the design is completed, based on the light-curing integrated molding technology, the light-curing prototype is designed in detail according to the final mold design, and the necessary auxiliary process structures are added, such as the casting shell, etc., to manufacture the resin prototype and the casting shell, and then use the gel The method of injection molding produces a ceramic (AL-series) mold that meets the design, and then completes the directionally solidified superalloy complex structure in a vacuum directional solidification furnace (three chambers, including a vacuum melting chamber, a heat preservation chamber and a cooling chamber), such as blades. Directed growth.

The specific method is: use the final formwork design, complete the corresponding resin prototype and pouring shell design in UG software, and then manufacture the resin prototype and pouring shell in the light curing molding machine; then prepare Al that meets the strength and performance requirements. -It is a ceramic slurry, using the resin prototype and casting shell to cast the ceramic mold shell, and after curing, drying, pre-sintering and final sintering, the final ceramic casting mold entity is obtained; finally, the single crystal turbine blade is manufactured in a vacuum directional solidification furnace product.

The main control points of ceramic shell preparation:

1) Raw materials and equipment. The raw materials used for preparing ceramic molds must be stored in closed packaging bags or sealed packaging barrels, and stored in a dry and ventilated environment. The raw materials for preparing ceramic shells mainly include coarse particles (40μm) and fine particles (2-5μm or nanoscale) alumina powder, magnesium oxide mineralizer, deionized water, acrylamide, methylenebisacrylamide, Sodium polyacrylate (concentration of about 18%), polyethylene glycol, ammonium persulfate (concentration of about 30%), tetramethylhexamethylenediamine (concentration of about 25%) and concentrated ammonia water, etc. The equipment used mainly includes light curing rapid prototyping machine (SPS450B), ball mill, gel injection molding machine, vacuum freeze dryer and vacuum pressure impregnation machine.

2) Photocuring prototype design and preparation. The design of the light-curing prototype is completed in UG software, and the casting fillet R0.5~1 is added according to GB/T6414-1999. Based on the three-dimensional modeling of single crystal turbine blades, determine the pouring position and design the pouring riser according to the function and shape of the components. Then add a pouring shell outside the pouring system. The shell is used to ensure the shape and thickness of the ceramic shell. In order to ensure that the entire resin prototype has sufficient strength after the ceramic slurry is filled, the thickness of the resin shell is 1-2mm, and reinforcement is added to the pouring shell. The ribs are 1mm thick and 3-5mm wide. After the above design is completed in the UG software, the data is exported by STL driving, and the export setting triangle tolerance is 0.05, the adjacent tolerance is 0.05, and the normal line is automatically generated. Then import the STL file into the Magics software to extract the shell, add support, and export the SLC file. Load the SLC file into the RPbuild software of the light-curing molding machine, and control the light-curing molding machine to automatically prepare resin parts. After the preparation is completed, remove the auxiliary support of the resin part, and clean the resin prototype 2 to 3 times with industrial alcohol to ensure that the residual liquid resin is completely cleaned up. Note: The blade prototype is manufactured separately from the cast shell and assembled together, this allows for easy cleaning of the resin prototype and ease of post-processing the blade prototype surface.

3) Preparation of ceramic slurry

This process begins with the preparation of the master mix. Calculate the volume of deionized water based on the volume of the light-curing resin mold and the solid phase content of the ceramic powder particles, and then add organic monomers (acrylamide or its substitutes), cross-linking agent (methylenebisacrylamide) and Dispersant (sodium polyacrylate), etc., stir to dissolve, adjust the pH value of the solution with concentrated ammonia water, keep it in the alkaline range (10-11), and finally obtain a premixed solution with an organic concentration of 20%. A water-based ceramic slurry is then prepared. Add the ceramic powder to the premix in batches, add 2 to 3 times the mass of balls, and ball ink for more than 1.5 hours to obtain a ceramic slurry with a viscosity of less than 1Pa·S and a solid volume fraction of 58 to 63vol%.

4) Preparation of ceramic mold

First complete the production of the green body, that is, add the catalyst (tetramethylhexamethylenediamine) and initiator (ammonium persulfate) to the ceramic slurry in sequence, and make it quickly and evenly dispersed, and then place the resin mold in the vibrating grouting machine , the vibration frequency is 30Hz-60Hz, inject ceramic slurry (this process must keep the flow of ceramic slurry steady and slow to ensure the smooth discharge of air bubbles in the slurry), and obtain ceramic green body. Then freeze dry under vacuum. The purpose of freeze-drying is to directly change the moisture in the green body from solid to gaseous, so that the shrinkage of the ceramic mold can be controlled. The next step is to degrease and pre-sinter the ceramic mold (sintering temperature <1250°C). Then perform multiple impregnations (this step is not necessary, if the strength of the ceramic mold is sufficient, this step can be omitted). Finally, final sintering is carried out (sintering temperature 1350°C to 1550°C). Note: there is a certain amount of ashes inside the pre-sintered ceramic mold, use compressed air to clean the residual ash in the ceramic shell, and the pressure of the compressed air is less than 2MPa.

After obtaining a ceramic mold that meets the requirements of directional solidification, it is placed in a three-chamber vacuum directional solidification furnace for single crystal turbine blade casting.

Claims (10)

1. a method for manufacturing a single crystal turbine blade ceramic mold, is characterized in that, comprises the following steps: 1) According to the requirements of the grain orientation of the single crystal turbine blade, use the foundry finite element software to design a matching spiral crystal selector, including the number of turns of the spiral crystal selection section, the distance between adjacent spiral sections and the size of the crystal lifter; 2) Design the initial casting mold based on the single crystal hollow turbine blade with a spiral crystal selector, and import it into the casting finite element software for heat transfer and stress analysis; The shape of the outer wall of the mold shell is used to reduce the stress; according to the distribution of thermal stress at each time, the wall thickness that meets the thermal intensity and the minimum stress is selected, and the wall thickness is taken as the uniform wall thickness of the initial mold after stress relief, and the secondary mold; 3) Place the designed secondary mold in the simulation environment of directional solidification for heat transfer analysis, and obtain the heat transfer law and temperature gradient distribution of the secondary mold. For the sudden change of the section, the mold strength is used as the initial boundary condition , through topology optimization, design the heat transfer channel, improve the heat transfer capacity at the sudden change in the cross section, and form a tertiary casting mold; 4) Then repeat the heat transfer analysis, stress analysis and directional solidification simulation analysis for the three casting molds, and modify them until the temperature gradient requirements of the compound directional solidification at the variable cross-section, and can withstand the stress in the process of directional crystal growth, to obtain the shape casting type; 5) Manufacture the resin prototype mold through the light curing rapid prototyping technology of the designed mold, and use the method of gel injection molding to manufacture the single crystal turbine blade ceramic mold. 2. the manufacture method of single crystal turbine blade ceramic casting mold as claimed in claim 1, is characterized in that, described turbine blade resin model with spiral crystal selector and initial mold are designed and constructed in UG software. 3. the manufacture method of single crystal turbine blade ceramic mold as claimed in claim 1 is characterized in that, the turbine blade resin model integrated manufacturing with spiral crystal selector, the spiral crystal selector CAD model assembly that will design On the CAD model of the blade, use modeling software to perform shelling processing on the three-dimensional model of the part, and the solid part is hollowed out, and the thickness of the shell is 0.6-3mm, and then the laser-cured rapid prototyping equipment is used to produce a spiral crystal selector. Turbine blade resin prototype. 4. The manufacturing method of single crystal turbine blade ceramic casting mold according to claim 1, characterized in that, the form of stress relief in step 2) is to passivate the sharp part of the outer wall of the shell until the stress concentration is eliminated or Reduce stress concentration. 5. the manufacture method of single crystal turbine blade ceramic casting mold as claimed in claim 1, is characterized in that, described secondary casting mold is placed in the simulated environment of the directional crystal growth that ProCAST software provides and carries out radiation heat transfer analysis, in There are the following settings when building a preheating model in ProCAST software: 5.1) Set the heat transfer coefficient of castings and shells to 0; 5.2) Set the heat transfer boundary condition on the surface of the formwork, set VIEW FACTOR to ON and set the radiation rate; 5.3) Set the casting to EMPTY, and set the casting status to FULL; After completing the preheating calculation through the preheating model, use the temperature distribution results of the mold shell to establish a calculation model for radiation heat transfer analysis, including the following settings: 5.4) Extract the temperature distribution state of the formwork in the preheating calculation; 5.5) Change the zero heat transfer coefficient of castings and mold shells; 5.6) Remove the heat transfer boundary condition on the inner surface of the mold shell, and set the casting state to FULL; Carry out radiation heat transfer analysis on the calculation model of radiation heat transfer analysis. During the analysis, the alloy material parameters of the castings are calculated using the Lever model, and the VIEW FACTOR is set to ON. The operating parameters are set in the Radiation module in the radiation heat transfer calculation. , corresponding to the radiation button box and the formwork; After the radiation heat transfer analysis is completed, the temperature distribution and heat transfer law of the mold shell and castings are obtained, that is, the temperature field distribution map; the temperature gradient is calculated according to the temperature distribution and the model, and the temperature gradient distribution map is obtained; combined with the thermal stress field distribution , Temperature field distribution and temperature gradient distribution, conduct comprehensive analysis to guide mold design. 6. The manufacturing method of single crystal turbine blade ceramic casting mold as claimed in claim 5, characterized in that, the moving rate of said radiation button box is set to the solidification rate of molten metal for casting. 7. the manufacture method of single crystal turbine blade ceramic casting mold as claimed in claim 1, it is characterized in that, design initial ceramic casting mold, utilize finite element software to carry out heat transfer and grain structure analysis in directional solidification process, for section The ceramic mold shell at the sudden change is thick, the heat transfer capacity is reduced, and it is easy to cause crystal defects. Taking the mold strength as the initial boundary condition, the mold structure is improved through topology optimization, and the heat transfer channel is designed to improve the heat transfer capacity at this place. 8. the manufacture method of single crystal turbine blade ceramic casting mold as claimed in claim 1, is characterized in that, described by light-curing rapid prototyping technology to manufacture resin prototype mold is: The design of the light-curing resin mold is completed in UG software. Based on the finalized casting mold, the pouring position is determined according to the function and shape of the component, and the pouring riser is designed; and the casting fillet R0.5~1 is added according to GB/T6414-1999; The cured resin mold is added with a pouring shell, the shell is 1-2mm thick, and reinforcing ribs are added to the shell; After the design of the light-curing resin mold is completed, it is exported in STL form, and then the STL file is imported into the Magics software to extract the shell, add supports, and export the SLC file; load the SLC file into the RPbuild software of the light-curing molding machine, and control the automatic curing of the light-curing molding machine. Preparation of resin parts; After the preparation is completed, remove the auxiliary support of the resin part, and clean the resin prototype with alcohol for 2 to 3 times to ensure that the residual liquid resin is completely cleaned up. 9. the manufacture method of single crystal turbine blade ceramic mold as claimed in claim 1, is characterized in that, described gel injection molding adopts the following method to carry out the preparation of ceramic slurry: 1) Calculate the volume of deionized water based on the volume of the light-curing resin mold and the solid phase content of the ceramic powder particles, then add organic monomers, crosslinking agents and dispersants in sequence, stir to dissolve, and adjust the pH of the solution with concentrated ammonia water 10 to 11 to obtain a premix solution with an organic concentration of 20%; 2) Add the ceramic powder to the premix solution in batches, add 2-3 times the mass of balls, and ball ink for about 1 hour to obtain a ceramic slurry with a viscosity of less than 1Pa·S and a solid phase volume fraction of 58-63vol%; The ceramic powder mainly includes coarse-grained alumina powder with a particle size of 40 μm, fine-grained alumina powder with a particle size of 2-5 μm, and a magnesium oxide mineralizer. 10. the manufacture method of single crystal turbine blade ceramic mold as claimed in claim 1, is characterized in that, the method for described gel injection molding prepares single crystal turbine blade ceramic mold comprises: 1) Add the catalyst and the initiator to the ceramic slurry in turn, and make it quickly and uniformly dispersed, then place the resin prototype mold in a vibrating grouting machine with a vibration frequency of 30Hz-60Hz, and inject the ceramic slurry to obtain a ceramic green body; Then freeze-dry under vacuum, so that the moisture in the ceramic biscuit is directly transformed from solid state to gaseous state; 2) Then remove the resin from the ceramic green body, pre-sinter after removing the resin, the pre-sintering temperature is <1250°C; there is a certain amount of ashes inside the pre-sintered ceramic mold, and the residual ash in the ceramic shell is cleaned with compressed air. Cleaning, the compressed air pressure is less than 2Mpa; 3) Finally, final sintering is carried out at a sintering temperature of 1350°C to 1550°C to obtain a ceramic mold.

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