CN102169518A - Accurate forming method for precise-casting turbine blade die cavity - Google Patents

Abstract

The invention discloses a precision casting method for determining the mold cavity of a turbine blade. According to the pouring process of the turbine blade, the pouring system model of the turbine blade is designed and the pouring experiment is carried out; The actual temperature at the back and the blade basin, determine the interface heat transfer coefficient, carry out the numerical simulation of the pouring process, obtain the deformation of the turbine blade casting during the pouring process, and carry out the numerical simulation of the precision casting process after the casting model is reversely deformed; the final judgment Whether the surface deviation meets the accuracy requirements of casting dimensional tolerances. The invention greatly improves the yield of turbine blades and reduces the period and times of mold testing.

Description

Precision Casting Method for Turbine Blade Die Cavity Determination

technical field

The invention relates to a shaping method of a mold cavity.

Background technique

Complex hollow turbine blades are the core technology of high thrust-to-weight ratio engines. This type of turbine blades is the key to the development of aero-engines due to their complex internal cooling structure, strict requirements on aerodynamic shape and blade wall thickness and dimensional accuracy, and harsh working conditions. At present, hollow turbine blades are generally precision cast with single crystal or directional crystal without margin. When the superalloy is injected into the mold shell, it will shrink and deform as the temperature decreases. The mold cavity used in investment casting must consider the compensation for the shrinkage deformation of the casting. Since the turbine blade is an ill-conditioned structure composed of a large number of free-form surfaces and a complex inner cavity, the shrinkage of the casting caused by uneven heat dissipation during cooling is nonlinear and non-uniform. As a result, the precision casting mold used to manufacture turbine blades has become the blade tooling with the longest design and manufacturing cycle and the most technical difficulty in engine development and production preparations, and the cavity design of precision casting molds is the key link to solve precise shape control.

The design principle of the mold cavity is to give an appropriate amount of anti-deformation at the deformed part to offset the shrinkage deformation of the casting during solidification and cooling. The shrinkage deformation of the casting is nonlinear, and it is reflected in the form of the displacement field (distribution of the deformation of the blade casting). How to obtain the displacement field of the casting and optimize the cavity of the mold based on it is a key to ensure the dimensional accuracy of the precision casting of the blade. At present, the design of the mold cavity still adopts the comprehensive shrinkage rate calculation profile in the three directions of X, Y, and Z according to the linear method. Obviously, this method is unreasonable. Due to the complex shape of the blade, the heat dissipation is uneven when the casting is cooled, so the deformation of each point of the blade is not consistent. It must be repeated many times to repair the mold and try the mold to obtain the precision requirement. The product. Therefore, this kind of inaccurate anti-deformation treatment design has many mold cavity trials, and the mold manufacturing cycle is long, which cannot meet the requirements of short mold production cycle and high precision. With the use of large-scale finite element analysis software for actual processing and production, there is currently a mold cavity design method that uses numerical simulation to quantify anti-deformation treatment (Chinese patent application number: 200710028749.7, application date June 22, 2007), for Improving the efficiency of mold design and reducing the manufacturing cycle play a certain role. However, the relaxation factor used in the anti-deformation algorithm is still determined empirically, and this method is still difficult to be directly used in the production process.

Contents of the invention

In order to overcome the deficiency that the prior art cannot accurately design the cavity of the mold, the present invention provides a method for designing the cavity of the precision casting mold based on numerical simulation, and the result can be directly used in the design of the cavity of the precision casting mold of the turbine blade, solving the problem The problem of long mold design cycle, low efficiency and low precision.

The technical solution adopted by the present invention to solve its technical problems comprises the following steps:

step 1

The pouring system model of the turbine blade is designed according to the pouring process of the turbine blade.

step 2

The finite element analysis method is used to divide the gating system model established in step 1 into units.

step 3

作为求解界面换热系数的数学模型。式中：T(h_c)为仿真温度值，_T′为与T(h_c)对应的测量温度值，n为布置的热点偶个数，即未知界面换热系数个数。建立迭代关系式T^k+1＝T^k+ΔT。式中：T^k+1为第k+1次迭代结果，T^k为第k次迭代的结果，ΔT为第k次迭代时的修正值，当数值模拟的计算温度值T(h_c)与测量温度值之差的绝对值|T^k-T′|小于指定的精度要求(可以取为10^-3)时，即迭代结果趋近于测温点温度时，有

，则认为此时数值模拟中的换热情况与实际相符，进而确定界面换热系数h_c。The gating system model established in step 1 was used to carry out the gating experiment. Use thermocouples to measure the actual temperature at the front and rear edges of the blade, the back of the blade and the leaf pot during the pouring and solidification process, and introduce the formula

As a mathematical model for solving the interface heat transfer coefficient. In the formula: T(h _c ) is the simulated temperature value, _T′ is the measured temperature value corresponding to T(h _c ), n is the number of arranged hot spots, that is, the number of unknown interface heat transfer coefficients. An iterative relationship T ^k+1 =T ^k +ΔT is established. In the formula: T ^k+1 is the result of the k+1 iteration, T ^k is the result of the k iteration, ΔT is the correction value of the k iteration, when the calculated temperature value T(h _c ) of the numerical simulation and When the absolute value |T ^k -T′| of the difference between the measured temperature values is less than the specified accuracy requirement (can be taken as 10 ^-3 ), that is, when the iterative result approaches the temperature of the temperature measurement point, there is

, it is considered that the heat transfer in the numerical simulation is consistent with the actual situation at this time, and then the interface heat transfer coefficient h _c is determined.

step 4

Accurate interface heat transfer coefficient is obtained through step 3, and then the numerical simulation of the pouring process is carried out to obtain the deformation of the turbine blade casting during the pouring process. Firstly, the numerical simulation boundary conditions are applied, including the thermophysical parameters of the alloy material and the mold shell material, the alloy temperature of the initial pouring, the alloy temperature at which the numerical calculation is terminated, the interface heat transfer coefficient between the alloy material and the precision casting mold shell, and the constraint conditions of the model displacement . Through the solution of the stress field in the precision casting process, the stress distribution of each node of the turbine blade mesh model in the precision casting process is obtained, and then the displacement of each node is derived, and the displacement field model can be established.

step 5

对铸件模型进行反变形处理。公式中P₀(x₀，y₀)表示初始叶片表面上任意离散点的坐标，

表示模具型腔上的任意一个离散点坐标，K表示离散点对应的收缩率，这里可以取为涡轮叶片模具型腔修模时所用的经验收缩率K为1.012，

表示浇注方向的铸件同一高度的剖面上两个离散点的坐标差比值，W_xy(x₁，y₁)表示两个离散点之间的位移变化量。Based on anti-morphing iterative formula

Deform the cast model. In the formula, P ₀ (x ₀ , y ₀ ) represents the coordinates of any discrete point on the initial blade surface,

Represents the coordinates of any discrete point on the mold cavity, and K represents the shrinkage rate corresponding to the discrete point. Here, it can be taken as the empirical shrinkage rate K used when the turbine blade mold cavity is repaired, which is 1.012.

Indicates the ratio of the coordinate difference between two discrete points on the section at the same height of the casting in the pouring direction, W _xy (x ₁ , y ₁ ) represents the displacement change between the two discrete points.

step 6

In step 5, the discrete points of the casting model after the inverse deformation treatment are obtained, and the inverse deformation model is obtained after surface reconstruction, that is, the mold cavity model. In order to verify whether the mold cavity model meets the requirements, the numerical simulation of the investment casting process is carried out under the same process conditions and mold structure as step 4.

step 7

Register the anti-deformation model obtained in step 6 with the casting design model to obtain the profile deviation of the anti-deformation model, and judge whether the profile deviation meets the accuracy requirements of the casting dimensional tolerance. If the accuracy requirements are met, the final anti-deformation model is the cavity of the precision casting mold. If the accuracy requirements are not met, repeat steps 4 to 7 until the final deformed model meets the accuracy requirements.

The beneficial effects of the invention are: through the optimized design of the mold cavity of the precision casting turbine blade, the finished product rate of the turbine blade is greatly improved; and the period and times of mold trial are reduced. This method has important theoretical significance and application value for the design of mold cavity. This method avoids the shortcomings of traditional experience design, and has the characteristics of short design cycle, high precision and high efficiency, and the defects of mold design can be analyzed in real time on the computer. It is found and corrected, which shortens the mold development cycle and significantly reduces the cost of mold design, especially for the development of new products that have no experience to follow. This method is suitable for the design of the outer cavity of the precision casting mold for turbine blades used in aero-engines. Compared with the technology of patent 200710028749.7, the present invention solves the problem that the current numerical simulation results are unreliable and can only be qualitative but not quantitative. At the same time, different relaxation factors are used for each grid node, which improves the accuracy of anti-deformation compensation.

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Description of drawings

Figure 1 is a flow chart of the present invention.

Figure 2 is a precision casting turbine blade model.

Figure 3 is a gating system model.

Figure 4 is a schematic diagram of thermocouple distribution.

Detailed ways

The embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings: this embodiment is implemented on the premise of the technical solution of the present invention, and provides detailed implementation methods and processes. But the scope of protection of the present invention is not limited to the following examples.

The design of the shaping mold cavity of producing certain type aviation turbine blade, embodiment step is as shown in Figure 1:

step 1

A certain type of turbine power blade is used for numerical simulation, as shown in Fig. 2. Its main parameters are blade body length 101mm, maximum chord length 59.21mm, maximum inscribed circle radius 5.67mm, leading edge radius 4.22mm, and trailing edge radius 1.27mm. The blade is made of the second generation single crystal superalloy DD6, and the mold shell is made of silica sand. According to casting feeding theory and actual production experience, the blade casting process and gating system are designed for power blades, using top injection, 3 pieces in a group. As shown in Figure 3.

step 2

The commercial finite element pre-processing software Hypermesh (product of Altair, USA) is used to divide the model into units based on non-uniform mesh division technology. First, the gating system model is imported into Hypermesh, and it is discretized into tetrahedral units, and the unit quality meets general requirements. Enterprise finite element analysis quality requirements, in this embodiment, require more than 95% of the unit quality to meet: unit warpage less than 5.0, unit long and short side ratio less than 5.0, skew less than 60.0, unit Jacob's ratio greater than 0.7. The total number of tetrahedral units is 1.645 million.

step 3

Using the pouring system established in step 1, set up a temperature field experiment to measure the temperature field of the turbine blade during the pouring and solidification process. After the wax mold is finished, wooden sticks are used to replace the fixed position of the thermocouple, and after the shell is made, a preset hole for the thermocouple is reserved at the fixed position. The location of the thermocouple is shown in Figure 4. A total of 14 sets of thermocouples were arranged in the experiment to measure the temperature change data of the tenon of the blade, the blade body and the seeding section respectively. Among them, 4 sets of thermocouples are placed in the seeding section, as shown in Figure 4. No. 1, 5, 6, and 10 thermocouples, No. 1 and 10 thermocouples measure the bottom temperature of the seeding section, and No. 5 measures the spiral temperature of the seeding section. The temperature at the junction of the seeding section and the blade body was measured on the 6th. 7 sets of thermocouples are placed in the blade body, as shown in Figure 4, No. 2 and No. 3 thermocouples are placed on the central axis of the leaf basin, No. 7, 8 and 9 thermocouples are located at the trailing edge, No. The central axis of the back of the body. Three sets of thermocouples are placed on the mortise. As shown in Figure 4, No. 4 thermocouple is located on the central axis of the blade, No. 13, No. 14 and No. 4 thermocouples are located on the same horizontal line, and the measured positions of the two sets of thermocouples are the same, but No. Shallower than hot spot No. 14. According to the position arrangement of the thermocouples used in the experiment, the temperature gradient during the solidification process of the blade can be measured, and the temperature difference at different positions (leaf pot, leaf back, and trailing edge) at the same level can also be measured. Using gravity pouring method. The pouring temperature is 1550°C, and the temperature field of six groups of blades is measured in the experiment. The data acquisition time is 4000 seconds, and the acquisition temperature range is 1550°C-600°C. Based on the reverse calculation module of ProCAST (a product of ESI Group in France), input the measured value, and after 15 iterations, reversely obtain the curve of the heat transfer coefficient of the casting and the mold shell as a function of time t, and obtain the casting and mold shell by curve fitting Functional expression of interfacial heat transfer coefficient: h _{casting - mold shell} = 12160.36+1245.61t ^-0.52 .

step 4

ProCAST is used to simulate the precision casting process of turbine blades. The alloy is DD6 high-temperature nickel-based alloy with a liquidus temperature of 1380°C and a solidus temperature of 1310°C. Its thermal conductivity is 33.2W/m·K, its density is 8780kg/m ³ , and its specific heat is 99.0KJ/Kg/K. The mold shell is made of silica sand with a thermal conductivity of 0.59W/m·K, a density of 1520kg/m ³ and a specific heat of 1.20KJ/Kg/K. The initial temperature of the alloy in the numerical simulation is 1550°C, and the alloy temperature at the end of the numerical simulation is 600°C. The interface heat transfer coefficient between the alloy and the mold shell is selected from the calculated value in step 3 of the embodiment. The displacement constraints are fixed at the bottom of the sprue and at the bottom of the blade seeding section and at the bottom of the cold copper.

step 5

对铸件模型进行反变形处理。公式中表示模具型腔上的离散点，K表示每个离散点对应的收缩率。为1.012，表示截面线上两个离散点的坐标差比值，W_xy(x₁，y₁)表示离散点的位移变化量，P₀(x₀，y₀)表示初始叶片截面离散点的坐标。Based on anti-morphing iterative formula

Deform the cast model. formula Represents the discrete points on the mold cavity, and K represents the shrinkage rate corresponding to each discrete point. is 1.012, Indicates the ratio of the coordinate difference between two discrete points on the section line, W _xy (x ₁ , y ₁ ) represents the displacement variation of the discrete point, P ₀ (x ₀ , y ₀ ) represents the coordinates of the initial blade cross-section discrete point.

step 6

In step 5, the discrete points of the casting model obtained after anti-deformation processing are obtained, and the anti-deformation model is obtained after using the surface reconstruction function under UG (a product of Siemens, Germany), that is, the mold cavity model. In order to verify whether the mold cavity model meets the requirements, the numerical simulation of the investment casting process is carried out under the same process conditions and mold structure as step 4.

step 7

Import the anti-deformation model obtained in step 6 into the UG platform through the "Import" function under the "File" menu of the UG software, and obtain the surface deviation of the anti-deformation model after registration with the casting design model. Detect whether the deformed model of the anti-deformation model meets the precision requirements of the casting. If the accuracy requirements are met, the cavity of the precision casting mold is designed according to the final reverse deformation deformation model. If the accuracy requirements are not met, the casting reverse deformation processing and numerical simulation will continue until the final reverse deformation model is deformed and the model meets the accuracy requirements.

Claims (1)

1. the accurate method for shaping of smart casting Mould Cavity for Turbine Blade is characterized in that comprising the steps:

Step 1

Design the running gate system model of turbo blade according to the pouring technology of turbo blade;

Step 2

The running gate system model that adopts finite element method that step 1 is set up carries out dividing elements;

Step 3

The running gate system model that adopts step 1 to set up is poured into a mould experiment; Adopt the actual temperature at thermocouple measurement blade front and rear edge, blade back and leaf basin place in cast and process of setting, introduce formula As the mathematical model of finding the solution interface heat exchange coefficient, in the formula: T (h _c) be the simulated temperature value, _{T '}For with T (h _c) corresponding measurement temperature value, the thermocouple number of n for arranging; Set up iterative relation formula T ^K+1=T ^k+ Δ T is in the formula: T ^K+1Be the k+1 time iteration result, T ^kBe the result of the k time iteration, the modified value when Δ T is the k time iteration is as the accounting temperature value T of numerical simulation (h _c) with the absolute value of the difference of measuring temperature value | T ^k-T ' | when requiring, T is arranged less than specified accuracy ^K+1=T ' thinks that then the heat exchange situation in numerical simulation this moment conforms to actual, and then definite interface heat exchange coefficient h _c

Step 4

Obtain accurate interface heat exchange coefficient by step 3, carry out the numerical simulation of casting process then, to obtain the turbo blade casting deformation situation in the casting process: at first apply the numerical simulation boundary condition, comprise the thermal physical property parameter of alloy material and formwork material, initial cast alloy temperature, end the interface heat exchange coefficient between alloy temperature, alloy material and the finish cast die shell of numerical evaluation, the constraint condition of model displacement; By finding the solution of essence casting process stress field, draw the stress distribution of smart each node of casting process turbo blade grid model, and then derive the displacement of each node, can set up the displacement field model.

Step 5

Based on the reversible deformation iterative formula Cast model is carried out reversible deformation handle P in the formula ₀(x ₀, y ₀) any coordinate of discrete point on the initial blade surface of expression,

Any one discrete point coordinate on the expression mold cavity, K represents the shrinkage factor of discrete point correspondence, getting K is 1.012,

The coordinate difference ratio of two discrete points on the section of the foundry goods sustained height of expression cast direction, W _Xy(x ₁, y ₁) displacement variable between two discrete points of expression;

Step 6

Discrete point after obtaining the cast model discrete point carried out reversible deformation and handle in step 5 carries out obtaining the mold cavity model behind the surface reconstruction; Under the prerequisite of process conditions identical and mould structure, carry out the numerical simulation of smart casting process with step 4;

Step 7

Reversible deformation model that step 6 is obtained and foundry goods design a model and obtain the profile departure of reversible deformation model behind the registration, judge whether the profile departure meets the accuracy requirement of the dimensional tolerance of casting; As meeting accuracy requirement, then final reversible deformation model is the die cavity of precision casting mould; As do not meet accuracy requirement, and repeating step 4～step 7 then, the model behind final reversible deformation model deformation meets accuracy requirement.

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