CN117733068A - Variable thickness casting mold and preparation method thereof, parameter measurement and parameter calibration method - Google Patents

Abstract

The invention provides a variable thickness casting mold and its preparation method, parameter measurement and parameter calibration method. The preparation method of the variable thickness casting mold includes: providing a rod-shaped runner wax mold; and providing a plurality of flake waxes of equal thickness or variable thickness. Mold, form a plurality of grooves at equal intervals along the length direction on the rod-shaped sprue wax mold, insert the sheet wax mold into the grooves and bond them to form a group tree; in order from bottom to top, start from the first layer of The wafer-like wax mold begins to undergo a step-by-step layering slurry-dipping and sand-dipping process in sequence, and the slurry-dipping position is gradually increased by one group tree spacing along the direction of the tree grouping each time or every interval, until the last layer of flake wax mold; The trees are uniformly sealed and dried under blowing conditions; the trees are dewaxed to obtain variable thickness molds. The invention can quickly, efficiently and material-savingly prepare variable thickness shells and shell test pieces, and achieve accurate measurement of mechanical performance parameters of ceramic shells and efficient and accurate calibration of interface heat transfer coefficients.

Description

Variable thickness casting mold and its preparation method, parameter measurement and parameter calibration method

Technical field

The present invention relates to the technical field of precision casting, and specifically to a variable thickness casting mold and its preparation method, parameter measurement and parameter calibration method.

Background technique

During the precision casting process, there is a complex mechanical interaction between the yielding and collapsible mold shell and the viscoelastic plastic metal. The casting shrinks and deforms during the cooling process, and is hindered by a certain mold shell and undergoes dimensional changes. The computer simulation technology of the solidification process predicts the dimensional change rules and theoretical changes during alloy pouring, metal solidification, shelling and cutting of the pouring system by integrating a multi-process flow-thermal-solid coupling model to provide theoretical guidance for the specific anti-deformation of the mold. , which can effectively reduce the problem of casting size out-of-tolerance. However, the mechanical properties of the yielding and collapsible molded shells and the metal in the near-semi-solid region are difficult to accurately measure in a short time, and the influence of the shell-alloy interaction on the interface heat transfer coefficient is difficult to accurately calculate using digital models, resulting in Important parameters in the fluid thermosolid model, such as the stiffness and strength of the mold shell, the stiffness and plastic modulus of the alloy under different cooling rates, the recessiveness of the mold shell with different numbers of back layers - viscoelastic plastic alloys of different thicknesses under the interaction 4D interface heat transfer coefficient, etc., are difficult to obtain accurately. The accuracy of these parameters determines the accuracy of numerical simulation. For example, the stiffness and strength of the mold shell determine whether the pouring process is successful, whether the casting will undergo thermal cracking, and the amount of dimensional deformation of the casting and the counter-compensation amount of the wax mold cavity. One of the key factors; the change of heat transfer coefficient with different solidification stages and spatial positions determines the cooling behavior of the casting; the strength and stiffness of the fired shell not only affect the plastic deformation behavior of the casting and the dimensional accuracy after cooling, but also are related to Whether the mold shell will collapse during the pouring of molten metal, whether thermal cracking defects will occur during the cooling and shrinkage of the metal, etc.

Traditional shell performance testing methods usually require shells of different thicknesses and temperatures to be prepared and tested one by one. The shell manufacturing process of the precision casting process is long, and each preparation process often takes several weeks, which is cumbersome, time-consuming, and inefficient. At the same time, due to the difficulty in ensuring the process uniformity of the slurry and sand leaching process, the uniformity of the slurry and molding sand quality, and the uniformity of the roasting process during each test, the traditional method is difficult to obtain accurate and unified results under specific process conditions. It is difficult to obtain high-throughput data and derive practical rules and guidance based on the test data. The theoretical rule model is affected by the differences in shell performance fluctuations between each process test, alloy performance fluctuations, process parameters and production environment parameters. It is difficult to accurately construct due to the influence of fluctuations. The only way to explore and summarize the experimental rules is through a large number of repeated experiments.

In addition, laboratory mold preparation methods often fail to simulate the conditions during the actual casting process, so it may not be possible to accurately evaluate the stiffness and strength performance of the mold shell in actual applications. For obtaining the heat transfer coefficient, traditional methods generally use fixed values instead, without taking into account the influence of the setback properties of the mold shell with different numbers of back layers, different local shrinkage rates of the casting, and the gap or pressure formed between the mold shell and the alloy.

Contents of the invention

In view of the defects in the prior art, the purpose of the present invention is to provide a variable thickness casting mold and its preparation method, parameter measurement and parameter calibration method, which can effectively solve the problems of low efficiency, waste of materials and inability to ensure process uniformity in traditional testing methods. It also provides a more accurate and efficient high-throughput evaluation and testing method for fluid-thermal-solid coupling model parameters for the foundry industry.

According to a first aspect of the present invention, a method for preparing a variable thickness casting mold is provided, including:

Provide a stick sprue wax pattern;

Provide a plurality of flake wax patterns, form a plurality of grooves at equal intervals along the length direction on the rod-shaped runner wax pattern, insert the flake wax patterns into the grooves and bond them to form a tree;

According to the bottom-up order, starting from the first layer of flake wax mold, the step-by-step slurry and sand spraying process is carried out in sequence. The slurry position for each time or for a preset number of intervals is gradually raised by one tree group along the direction of the tree group. spacing, up to the last layer of flake wax pattern;

Carry out uniform sealing treatment on the group of trees and dry them under blowing conditions;

The tree is dewaxed to obtain a variable thickness cast.

Optionally, starting from the first layer of sheet wax mold, a step-by-step slurry and sand leaching process is performed sequentially, wherein: the slurry and sand leaching process includes sequentially making the surface layer, the middle layer and the back layer, and the back layer of each layer is After preparation, dry under blowing conditions. For example, for silicon oxide type shells, after the preparation of each back layer is completed, dry it under air blowing conditions for 4-12 hours; for an alumina type shell, after the preparation of each back layer is completed, dry it under air blowing conditions for 8 hours -16 hours.

Optionally, the tree group is subjected to dewaxing treatment, wherein: dewaxing is carried out at 150-200°C.

According to a second aspect of the present invention, a variable-thickness casting mold is provided, which is prepared by using the above-mentioned variable-thickness casting mold preparation method.

According to a third aspect of the present invention, a method for measuring mechanical property parameters of ceramic mold shells is provided, which method includes:

After cutting and polishing the above variable thickness casting mold along the root of the test piece, shell test pieces with different thicknesses are obtained;

The molded shell test pieces are uniformly placed in a mold shell roasting furnace and roasted to simulate the one-time baking process of a real precision casting shell, and obtain molded shell test pieces with different numbers of back layers;

Put the molded shell test pieces with different numbers of back layers into the three-point bending tester to simulate the secondary baking process of the molded shell. By moving the test bench, conduct three-point bending test on multiple shell test pieces with different thicknesses one by one. Bending test was performed to obtain the mechanical performance parameters of the casting in the fluid-thermal-solid coupling model.

According to a fourth aspect of the present invention, a method for calibrating interface heat transfer coefficient is provided, which method includes:

The above-mentioned variable-thickness casting mold is roasted once and the mold shell is preheated;

Set a thermocouple at the corresponding test piece of the variable thickness casting mold;

Transfer the variable thickness casting to the vacuum pouring furnace for pouring, and obtain the temperature-time data of the thermocouple during the pouring process;

According to the temperature-time data, the interface heat transfer coefficient-time curve data at each shell test piece was back-calculated, and the mechanical test results of the casting mold were brought into it. Combined with the numerical simulation method, the values of the shell test pieces with different thicknesses and Model the change of alloy-shell contact pressure and gap size with time at the interface of metal specimens with different alloy thicknesses, and establish a digital model of the change of interface heat transfer coefficient with time, interface gap and interface pressure.

Optionally, a thermocouple is installed in the center area of the variable-thickness casting mold corresponding to the test piece using a drilling method.

Optionally, after transferring the variable-thickness casting mold to a vacuum pouring furnace for pouring, and obtaining temperature-time data of the thermocouple during the pouring process, it also includes: cutting the metal test piece and observing the microscopic view of the metal test piece. organization, and conduct tensile mechanical tests on metal specimens.

Compared with the prior art, the present invention has at least one of the following beneficial effects:

On the basis of ensuring the uniformity of the process, the present invention can prepare molded shells with different numbers of back layers on the same group of trees at one time through layered slurry and sand leaching, and can quickly, efficiently and material-savingly prepare molded shells with variable thicknesses. Audition.

Furthermore, based on the variable thickness shell test piece prepared above, it is convenient to simultaneously measure the stiffness, strength, and thermal shrinkage rate of shells with different thicknesses on the basis of effectively realizing the fluctuation control of all process parameters, production environment, test conditions and other control variables. and other parameters, construct a regular model of the changes in the thermodynamic properties of the molded shell under the condition that different shell thicknesses are used as independent variables.

By preparing alloy test pieces of different thicknesses and variable thickness shell combinations on the same group of trees, the present invention can efficiently and accurately evaluate the thickness of the shell on the basis of effectively realizing the fluctuation control of all process parameters, production environment, test conditions and other control variables. The relationship between metal local shrinkage-temperature and interface heat transfer coefficient provides more accurate data support for the precision casting process.

Description of drawings

Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

Figure 1 is a schematic flow chart of a method for measuring mechanical property parameters of ceramic mold shells in an embodiment of the present invention;

Figure 2 shows the dipping slurry for different numbers of back layers in the high-throughput shell manufacturing process in one embodiment of the present invention: (a) prepare a rod-shaped wax pattern, (b) insert a sheet-shaped wax pattern to form a wax pattern tree, (c) The first four layers of grouting process, (d) the fifth layer of grouting process, (e) the sixth layer of grouting process, (f) the tenth layer of grouting process, (g) unified sealing process, (h) dewaxing Process, (i) prepared variable thickness shell;

Figure 3 is a schematic diagram of the testing method for high-throughput shell strength, elastic modulus, and damage mode in one embodiment of the present invention;

Figure 4 is a schematic flow chart of the calibration method of the interface heat transfer coefficient in an embodiment of the present invention;

Figure 5 is an overall schematic diagram of the preparation of variable thickness castings, measurement of mechanical properties parameters and calibration of interface heat transfer coefficient parameters in one embodiment of the present invention;

Figure 6 is a schematic structural diagram of a wax mold tree in an embodiment of the present invention; (a) is an overall schematic diagram, (b) is a cross-sectional schematic diagram, the black dots in the diagram represent the placement positions of the thermocouples, (c) is Top view schematic diagram, (d) is the main view schematic diagram;;

Figure 7 is a diagram showing the relationship between heat transfer coefficient, alloy state and shell-alloy interaction force in one embodiment of the present invention;

Figure 8 is a schematic diagram of a method for measuring the relationship between the heat transfer coefficient, the alloy state, and the shell-alloy interaction force using the variable-thickness shell/variable-thickness metal test piece group casting method in one embodiment of the present invention;

Figure 9 shows a series of calculation results of local alloy temperature-alloy/shell contact pressure produced by varying shell thickness and varying alloy test piece thickness in one embodiment of the present invention. Based on this, it can be combined with the temperature reduction data of thermocouples to achieve high-throughput Obtain the contact pressure-heat transfer coefficient functional relationship formula;

Figure 10 is a calculation result of a series of local alloy temperature-alloy/shell gap vertical distance produced by deforming the shell thickness and the deforming alloy test piece thickness in one embodiment of the present invention. Based on this, it can be compared with the cooling data of the thermocouple. Quantitatively obtain the alloy/shell gap-heat transfer coefficient functional relationship formula;

Figure 11 shows the parameters and the thermosolid coupling model of precision casting deformation obtained in one embodiment of the present invention.

Detailed ways

The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

Referring to Figure 1, an embodiment of the present invention provides a method for preparing a variable thickness casting mold. The method includes:

S1. Provide a rod-shaped sprue wax mold;

S2. Provide multiple flake wax patterns of equal thickness, and form multiple grooves at equal intervals along the length direction on the rod-shaped runner wax pattern. The size of the grooves matches the flake wax pattern. Insert the flake wax pattern into the groove. slot and bond to form a group tree;

S3. According to the bottom-up order, starting from the first layer of flake wax model, the step-by-step slurry-dipping and sand-dipping process is carried out. The slurry-dipping position is gradually increased by one along the direction of the tree group each time or every preset number of intervals. The spacing between groups of trees until the last layer of flaky wax mold; among them, the preset number is an integer greater than or equal to 1, which is determined according to the experimental requirements;

S4. Perform uniform sealing treatment on the group of trees and dry them under blowing conditions;

S5. Dewax the tree to obtain a variable thickness casting.

In the embodiment of the present invention, in step S1, the size of the rod-shaped runner wax mold can be adjusted according to actual needs and the characteristics of different shell materials, thereby providing greater flexibility for preparing different types and sizes of shell test pieces.

In step S2, for example, the rod-shaped sprue wax pattern is in the shape of a rectangular parallelepiped, which has four surfaces at the same height, and a groove is provided on each of the four surfaces for assembling the sheet wax pattern. In the calibration of the parameters of the fluid-thermal coupling model, the size of the sheet wax model cannot be too short in width, otherwise the heat dissipation effect at the edge of the test piece will exceed the influence caused by the change in the heat transfer coefficient of the upper and lower surface interfaces of the test piece. At the same time, the test piece The piece should not be too long, otherwise the test piece may fall off during the dipping process. The size of the flake wax pattern needs to be sufficient so that the shrinkage of the flake wax pattern along the thickness direction has a major impact on the interface contact. At the same time, the change in the interface contact causes a change in the interface heat transfer coefficient, which is directly reflected in the test piece. During the cooling process, the value of the 4D interface heat transfer coefficient can be calculated through the back calculation of the simulation calculation. In a specific embodiment, the width of the sheet wax mold is 1.5cm-3.5cm, the length is 3cm-15cm, and the thickness is 2mm-8mm. Of course, other sizes may also be used in other embodiments and are not limited thereto.

In some embodiments, in step S3, the stepwise layered dipping and slurrying process refers to performing the stepwise layered dipping and slurrying and sanding process in a bottom-up order starting from the first layer of the sheet wax model. The dipping position for each preset number of times or at each interval is gradually increased by one group tree spacing along the group tree direction until the last layer of flake wax mold. The slurry and sand pouring process includes sequentially making the surface layer, the middle layer and the back layer. Preferably, after the surface layer and the middle layer are completed, start from the back layer in a bottom-up order, starting from the first layer of sheet wax mold. The step-by-step slurry-dipping and sand-dipping process begins in sequence, and the slurry-dipping position is gradually increased by one tree group spacing along the direction of the tree group each time or every interval, until the last layer of flaky wax mold. A group of trees is formed on a rod-shaped wax mold, and during the slurry dipping process, the group of trees is not completely immersed in the slurry, and sand is poured uniformly. The layered method of dipping slurry and sand is used to achieve high-throughput on the same group of trees. Shell specimens with different numbers of back layers were prepared. After each backing layer is prepared, it is dried under blowing conditions. For example, for the silicon oxide type shell, after the preparation of each back layer is completed, it is dried under blowing conditions for 4-12 hours, preferably 8 hours. For another example, for an alumina type shell, after the preparation of each back layer is completed, it is dried under blowing conditions for 8-16 hours, preferably 12 hours. In this embodiment, through layered slurry and sand leaching, molded shells with different numbers of back layers can be prepared on the same group of trees at one time, and variable thickness shell test pieces can be prepared quickly, efficiently, and save materials.

In some embodiments, in step S4, the drying time is selected based on the principle of sufficient drying, such as 24 hours. Of course, it can also be other drying times. In step S5, dewaxing is performed at 150-200°C, preferably in an environment of 178°C. The minimum starting pressure is set to 8bar, the final decompression pressure is set to 2bar, and the dewaxing time is 20min; the above-mentioned slurry and sand leaching In the process, the corresponding drying time and shell baking temperature are adjusted for different shell materials (eutectic silicon oxide shell and single crystal alumina shell), so that the mold shell in the real precision casting process can be accurately simulated. Preparation process flow.

In another embodiment, the present invention also provides a variable-thickness casting mold, which is prepared by the above-mentioned preparation method of a variable-thickness casting mold. The shell test piece of the variable-thickness casting mold has different back layers. Number, the specific number of back layers can be set according to actual needs. The variable-thickness shell test pieces prepared by this method are conducive to the subsequent measurement of the stiffness, strength, and thermal shrinkage of shells with different thicknesses on the basis of effectively realizing the fluctuation control of all process parameters, production environment, test conditions and other control variables. rate and other parameters, and construct a regular model of the changes in the thermodynamic properties of the molded shell under the condition that different shell thicknesses are used as independent variables.

Based on the same inventive concept, embodiments of the present invention provide a method for measuring mechanical performance parameters of ceramic shells, including:

M1, cut the variable-thickness casting mold prepared above along the root of the test piece, ensure that the width of the mold shell test piece is the same through cutting, and polish the surroundings of the mold shell test piece, and prepare molds with different thicknesses through high-throughput Shell test pieces;

M2, place the cut and polished shell test pieces in a shell roasting furnace for baking to simulate the one-time baking process of a real precision casting shell, and obtain shell test pieces with different numbers of back layers;

M3, put the shell test pieces with different numbers of back layers into the three-point bending tester to simulate the secondary baking process of the shell, and test multiple shell test pieces with different thicknesses one by one by moving the test bench. Three-point bending test was performed to obtain the elastic modulus, strength, fracture strength and other mechanical performance parameters of the casting in the fluid-thermal-solid coupling model.

According to the embodiment of the present invention, variable thickness shell test pieces are prepared through high throughput. During the process of dipping the slurry and leaching the sand, the workers can skillfully ensure that the techniques are unified and have high consistency. On the basis of ensuring the unity of the process, a large number of products with different backgrounds can be produced. The layer-by-layer type shell test piece can be used for high-throughput measurement of parameters such as mechanical strength, stiffness, shrinkage and thermal conductivity of the type shell test piece.

The embodiment of the present invention performs three-point bending tests on shell test pieces with different thicknesses and different temperature conditions in the same experiment, ensuring the uniformity of different shell test pieces under the same primary and secondary baking conditions, which is helpful to Accurately evaluate the performance of the mold shell during the actual casting process. The results of mechanical property parameters such as elastic modulus, strength and fracture strength of the mold in the flow-thermal-solid coupling model obtained from the three-point bending test provide accurate mechanical parameter values of the mold and can determine the occurrence of the mold during the casting process. concessional deformation, as well as the contact between the mold and the casting, and combined with numerical methods to reversely calibrate the mathematical relationship between the interface heat transfer coefficient and the interface gap and pressure. The above results are used to calibrate the fluid-thermal-solid coupling calculation parameters. The yielding and collapsibility of the mold enables accurate calibration of the 4D heat transfer coefficient.

In a specific embodiment, continuing to refer to Figure 1, a high-throughput preparation method is used to prepare a molded shell test piece, and the mechanical property parameters of the ceramic molded shell are measured, which mainly includes the following steps:

1.1 Preparation of rod-shaped runner wax mold

First, the rod sprue wax pattern is prepared to the required size. The rod-shaped runner wax mold is used as a pouring system, so that multiple flake wax molds or wax molds of other shapes can be grouped at the same height, and the wax molds below the same height can be passed through the slurry liner by using the slurry liner. method to make a layer of mold shell, and the wax mold above this height will not be stained with slurry or sand. Specifically, the length of the rod-shaped sprue wax mold needs to be 3 to 15 times the side length of the cross-section, and the cross-section must be a square or other uniform polygon. The size requirement of the rod-shaped runner wax pattern is that the side length of the cross-section is greater than 1.5 times the width of the flake wax pattern, and the length must be able to meet the even arrangement of the flake wax pattern.

1.2 Prepare the groove and insert wax sheets of equal thickness

Prepare a sheet wax pattern with a width, length, and thickness of 60 mm × 30 mm × 5 mm. Use a soldering iron to prepare grooves at equal intervals on the rod-shaped runner wax pattern. The size of the grooves needs to match the size of the sheet wax pattern. After inserting the sheet wax pattern into the groove, use bonding wax to bond the sheet wax pattern and the rod-shaped sprue wax pattern.

1.3 Step layered slurry dipping and sand pouring process

Referring to Figure 2, the layered slurry process includes the production of the surface layer, the middle layer and the back layer. First apply the first layer (surface layer). Sink the entire shell into the slurry twice, and rotate the shell in the air after each dip until the slurry no longer drips. Then, perform the sand pouring operation in the sand pouring machine. For the eutectic silicon oxide shell, it needs to be dried for 5 hours after being dipped in slurry and sanded; for the single crystal alumina shell, it needs to be dried for 8 hours.

Then proceed to the production of the second and third layers (middle layers). The method of dipping the slurry and pouring the sand is the same as the first layer, but it needs to be done separately. The eutectic shell needs to be dried for 5 hours, and the monocrystalline shell needs to be dried for 8 hours.

The method of dipping slurry and sand for the fourth layer (back layer) is the same as before. Starting from the fifth layer, during each slurry dipping process, the upper boundary of the mold shell needs to be moved upward by one layer until it is unified after the tenth layer. Sealing grout, it needs to dry for 24 hours after sealing. After drying, dewaxing is performed.

1.4 type shell test piece cutting, grinding and primary roasting

Cut the prepared shell test pieces and polish them uniformly to ensure that the size of the shell test pieces is uniform. The cut shell test pieces are roasted once. For single crystal shells, the roasting conditions are 240 minutes to heat up to 1050°C, hold for 120 minutes, and then cool in the furnace; for polycrystalline shells, the roasting conditions are 135 The temperature was raised to 950°C in 120 minutes, kept at the temperature for 120 minutes, and then cooled in the furnace. The baking process of the molded shell test piece accurately simulates the primary baking process of the actual molded shell.

1.5 Type shell preheating process simulation and three-point bending test

Referring to Figure 3, the shell test pieces are uniformly placed in the test furnace of a three-point bending test instrument for heating. The temperature rise and insulation strategy is the same as the secondary baking conditions of the mold shell, simulating the secondary baking process of the mold shell. After reaching the heating and insulation conditions, multiple test pieces of different thicknesses are tested one by one by moving the test table. After the test, the temperature is lowered to other test temperature points and the measurement is continued by moving the sample table.

The embodiment of the present invention adopts a high-throughput measurement method to not only reduce the number of times of heating and holding, but also accurately simulates the cooling process of the mold shell after secondary baking. The measured stiffness and strength data can accurately reflect the mold shell in the real precision casting process. parameters such as stiffness and strength. On the basis of effectively realizing the fluctuation control of all process parameters, production environment, test conditions and other control variables, the stiffness, strength, thermal shrinkage and other parameters of molded shells with different thicknesses are simultaneously measured to construct the molded model with different shell thicknesses as independent variables. Regular model of changes in various thermodynamic properties of the shell.

Based on the same inventive concept, with reference to Figure 4, another embodiment of the present invention provides a method for preparing a variable thickness mold, including:

S1. Provide a rod-shaped sprue wax mold;

S2. Provide multiple flake wax patterns with variable thickness, form multiple grooves at equal intervals along the length direction on the rod-shaped runner wax pattern, insert the flake wax patterns into the grooves and bond them to form a tree;

S3. According to the bottom-up order, starting from the first layer of flake wax model, the step-by-step slurry-dipping and sand-dipping process is carried out. The slurry-dipping position is gradually increased by one along the direction of the tree group each time or every preset number of intervals. The spacing between groups of trees until the last layer of flaky wax mold; among them, the preset number is an integer greater than or equal to 1, which is determined according to the experimental requirements;

S4. Perform uniform sealing treatment on the group of trees and dry them under blowing conditions;

S5. Dewax the tree to obtain a ceramic mold with uniformly variable thickness.

In some embodiments, in step S2, the width of the sheet wax mold is 1.5cm-3.5cm, the length is 3cm-15cm, and the thickness is 2mm-8mm.

In step S4, the slurry and sand leaching process includes sequentially making the surface layer, the middle layer and the back layer; for the silicon oxide type shell, after the preparation of each back layer is completed, it is dried under blowing conditions for 4-12 hours, preferably , for 8 hours; for aluminum oxide type shells, after the preparation of each back layer, dry it under blowing conditions for 12 hours.

Based on the same inventive concept, the embodiment of the present invention provides a method for efficiently and accurately calibrating the parameters of the thermo-solid coupling model of precision casting flow. Specifically, the interface heat transfer coefficient is calibrated. Figure 5 shows the preparation method in one embodiment of the present invention. Overall schematic diagram of variable thickness casting, mechanical property parameter measurement and interface heat transfer coefficient calibration. The method includes:

S100, perform primary roasting and shell preheating on the above variable thickness casting mold;

S200, use the drilling method to set up the thermocouple at the center of the test piece of the variable thickness casting; the specific operation of the drilling method is: first use a drilling drill and other equipment to drill a hole with a diameter of 0.3-1mm and a depth of 1-3mm in the specified area. , select appropriate high-temperature resistant AB glue or other high-temperature resistant glue, fill the hole with A glue, and after inserting the K-type or S-type thermocouple, use B glue to fix the thermocouple in the hole;

S300, transfer the variable thickness mold to the vacuum pouring furnace for pouring, and obtain the temperature-time data of the thermocouple during the pouring process;

S400, based on the temperature-time data, reversely obtain the interface heat transfer coefficient-time curve data of each shell test piece, bring in the mechanical property parameters of the shell, and combine the numerical simulation and inverse method with different thickness shell test pieces and different The change curve of alloy-shell contact pressure and gap size at the interface of alloy thickness metal test piece (alloy test piece) with time is used to establish a digital model of the change of interface heat transfer coefficient with time, interface gap and interface pressure.

In the above embodiment, after the sheet-shaped wax pattern is dewaxed, the inner cavity of the casting mold retains the shape of the sheet-shaped wax pattern, so that after the casting process, a sheet-shaped metal test piece is formed. It should be noted that in some other embodiments, wax patterns of other shapes can also be used. In the high-throughput calibration process of interface heat transfer coefficient and mold mechanics, both casting mold test pieces and metal test pieces can be used. The cutting method maintains its shape, and other wax mold shapes can also be used to reversely calibrate the 4D interface heat transfer coefficient through simulation.

After pouring, cooling and solidification, the alloy test pieces at different positions have different cooling rates due to different shell thicknesses and alloy thicknesses. In some embodiments, the shell test pieces are transferred to a vacuum pouring furnace for pouring, and After obtaining the temperature-time data of the thermocouple during the pouring process, it also includes: cutting the metal test piece to observe the microstructure of the metal test piece, and performing a tensile mechanical test on the metal test piece. Through structural observation, the numerical model expression of the shell thickness-alloy thickness and the secondary diameter distance can be obtained with high throughput. Through tensile mechanical tests, the relationship between parameters such as elastic modulus/plastic modulus/strength of the alloy, the secondary diameter spacing and the temperature during testing can be established.

In the embodiment of the present invention, by conducting experiments on the same group of trees, strict control over the fluctuation of control variables is achieved, and the interface heat transfer coefficient can be calibrated more accurately.

Continuing to refer to Figure 4, in a specific embodiment, a high-throughput preparation method is used to prepare a shell test piece, and the relationship between the shell thickness-metal local shrinkage-temperature and the interface heat transfer coefficient is efficiently calibrated, which mainly includes the following steps :

1.1 Preparation of rod-shaped runner wax mold

First, the rod sprue wax pattern is prepared to the required size. The length of the rod-shaped sprue wax mold needs to be 3 to 15 times the side length of the cross-section, and the cross-section should be a square or other uniform polygon. The size requirement of the rod-shaped runner wax pattern is that the side length of the cross-section is greater than 1.5 times the width of the flake wax pattern, and the length must be able to meet the even arrangement of the flake wax pattern.

1.2 Prepare the groove and insert the variable thickness sheet wax mold

Prepare sheet wax molds with width, length, and thickness of 60mm×30mm×5mm, 60mm×30mm×10mm, 60mm×30mm×15mm, and 60mm×30mm×20mm respectively, and use a soldering iron to prepare them at equal intervals on the rod-shaped runner wax mold. Some grooves, the size of the grooves needs to fit the size of the sheet wax pattern. After inserting the sheet wax pattern into the groove, use bonding wax to bond the sheet wax pattern and the rod-shaped sprue wax pattern. After completion, attach the thermocouple to the surface of the sheet wax mold. The size of the prepared group tree is shown in Figure 6.

1.3 Step layered slurry dipping and sand pouring process

The layered slurry process includes the production of the surface layer, middle layer and back layer. First apply the first layer (surface layer). Sink the entire shell into the slurry twice, and rotate the shell in the air after each dip until the slurry no longer drips. Then, perform the sand pouring operation in the sand pouring machine. For the eutectic silicon oxide shell, it needs to be dried for 5 hours after being dipped in slurry and sanded; for the single crystal alumina shell, it needs to be dried for 8 hours.

Then proceed to the production of the second and third layers (middle layers). The method of dipping the slurry and pouring the sand is the same as the first layer, but it needs to be done separately. The eutectic shell needs to be dried for 5 hours, and the monocrystalline shell needs to be dried for 8 hours.

The method of dipping slurry and sand for the fourth layer (back layer) is the same as before. Starting from the fifth layer, during each slurry dipping process, the upper boundary of the mold shell needs to be moved upward by one layer until it is unified after the tenth layer. Sealing grout, it needs to dry for 24 hours after sealing. After drying, dewaxing is performed.

1.4 Primary roasting and shell preheating

The dewaxed shell is placed in a shell roasting furnace for primary roasting. Specifically, it is roasted at 1050°C for about 2 hours to simulate the primary roasting process of a real precision casting shell. For single crystalline shells, the baking conditions are: 240 minutes to heat up to 1050°C, hold for 120 minutes, and then cool in the furnace; for polymorphic shells, the firing conditions are: 135 minutes to heat up to 950°C, hold for 120 minutes, and then cool down. Furnace cools down.

After the first roasting, the mold shell is cooled in the furnace. Put the cooled mold shell into the shell preheating furnace to preheat for secondary roasting. The roasting temperature is about 1000°C and the roasting time is about 2 hours. After the secondary roasting, the mold shell should be transferred to the vacuum within 30 seconds. Pouring is carried out in a pouring furnace.

1.5 Pouring and temperature measurement experiment

Put the preheated shell and the temperature measuring black box into the vacuum pouring furnace at the same time. In this example, the alloy pouring temperature is 1500°C and the alloy type is K439B alloy. During the pouring process, the temperature measurement data is read and recorded in real time, and the temperature-time data of all thermocouples are obtained.

1.5 Pouring and temperature measurement experiment

After pouring, input the obtained temperature-time data into the ProCAST software. Use the heat transfer coefficient inverse module of ProCAST to obtain the interface heat transfer coefficient-time curve data of each test piece, and calculate the different values through numerical simulation. The change curve of alloy-shell contact pressure and gap size with time under the conditions of thick shell and different local alloy shrinkage rates, and fitting the relationship between shell thickness-metal local shrinkage-temperature and interface heat transfer coefficient, to establish Digital model of the interface heat transfer coefficient changing with time, interface gap, and interface pressure. Figure 7 is a schematic diagram reflecting the thermal coupling mechanism. Figure 8 is a schematic diagram reflecting the coupling effect of the specimen thickness and mold thickness on the interface heat transfer coefficient. , According to the schematic diagrams of the simulation results in Figures 9 and 10, it is shown that after the experimental process, the simulated data is continuously corrected by the experimental data to make the simulated data tend to the experimental data, and the accurate value of the interface heat transfer coefficient can be obtained.

The high-throughput calibration method of the 4D interface heat transfer coefficient in the embodiment of the present invention prepares a combination of different metal test piece thicknesses and mold shell thicknesses on the same group of trees, and utilizes the different local characteristics of different metal test pieces during the solidification process. The shrinkage rate, as well as the different concessional properties of different shell thicknesses, thereby obtaining a series of viscoelastic plastic metal-concessive shell interface states during the casting process, which are reflected in the gap formation or pressure state at the shell-alloy interface . Use a K-type or S-type thermocouple to measure the temperature change of the test piece during the solidification process, and use the obtained temperature data to use a reverse fitting method in casting simulation software such as ProCAST to obtain alloy test pieces of different thicknesses - different thickness mold shells The interfacial heat transfer coefficient of the interface changes with time, combined with the simulated change curves of the gap size and pressure value at the interface of alloy specimens of different thicknesses and shells of different thicknesses with time, and then the interface heat transfer coefficient changes with time. , digital model of changes in interface gap and interface pressure. Compared with the existing model in which the interface heat transfer coefficient changes with time or with the temperature of the alloy and mold side, this model directly establishes the relationship between the interface heat transfer coefficient and the interface gap, Interface pressure relationship, with higher accuracy. This model can be used for other castings and establish an accurate description of the shell-alloy interface. Bringing this model into the fluid thermo-solid numerical simulation model can improve the accuracy of temperature field simulation, thereby improving the accuracy of stress and deformation field simulation.

1.6 Microstructure observation and alloy mechanical testing

Since the structure of precision castings is mainly affected by the cooling rate, at the same time, in the actual production process, the cooling rate is affected by the thermal insulation capacity of the mold shell and the local thermal modulus. The local thermal modulus refers to the ratio of the local volume to the surface area. The greater the value, larger, indicating that the longer it takes to cool, the later the area solidifies. Adjusting the thickness of the test piece is one of the best ways to adjust the local thermal modulus.

In order to simulate different cooling conditions, cooling rate changes and casting structures under different cooling conditions in the real casting process, after the casting test, the metal specimens were cut and the microstructure was observed and tensile mechanical tests were performed. Specifically, the obtained alloy test piece set was used to create the casting, the alloy test pieces were cut one by one, and metallographic samples were prepared using inlay, grinding, and polishing techniques, and EBSD technology was used to record the results under different shell thicknesses and local thermal modulus conditions. The average grain size of the metallographic sample is etched, and the secondary dendrite spacing under different shell thickness and local thermal modulus conditions is observed and recorded through an optical microscope. The average grain size and the secondary diameter spacing value are fitted to obtain a digital model of the average grain size and the secondary diameter spacing value for different shell thicknesses and local thermal modulus. By measuring the stiffness, strength and plastic modulus values of different alloy test pieces under tensile conditions, a digital model of the stiffness, strength and plastic modulus of the alloy under different shell thicknesses and local thermal modulus conditions is obtained, as shown in the figure As shown in 11, these relational expressions can be directly embedded into the constitutive model of the thermo-solid coupling equation of precision casting mechanical deformation, which can quickly and efficiently calibrate precision casting stress deformation simulation.

On the basis of ensuring the uniformity of the process, the above-mentioned embodiments of the present invention can prepare mold shells with different numbers of back layers on the same group of trees at one time through layered slurry and sand leaching, and can quickly, efficiently and material-savingly prepare variable shells. Thickness shell test piece, so as to facilitate the simultaneous measurement of parameters such as stiffness, strength, thermal shrinkage rate, etc. of shells with different thicknesses.

In the numerical calculation of precision casting dimensions, the mechanical interaction between the metal and the casting mold and the accurate interface heat transfer coefficient value jointly affect the accuracy of the casting deformation simulation. This is the key significance of the fluid-thermal-solid coupling solution, that is, by The thermal effect affected by the boundary heat transfer coefficient affects the process of thermal shrinkage of the casting. At the same time, thermal shrinkage has an important impact on the interface contact between the casting and the casting mold contact interface, which in turn affects the interface heat transfer coefficient. The two influence and interact with each other, and high-throughput experiments must be conducted on one sample. In the above embodiments of the present invention, by preparing alloy test pieces of different thicknesses and variable thickness shell combinations on the same group of trees, the relationship between the shell thickness-metal local shrinkage-temperature and interface heat transfer coefficient can be efficiently and accurately evaluated, thereby providing a precise The casting process provides more accurate data support.

The above-mentioned embodiments of the present invention prepare variable-thickness casting molds through the method of gradient slurry and sand leaching, so that variable-thickness shell test pieces can be prepared at high throughput for high-throughput measurement of the stiffness, strength, and thermal shrinkage of precision casting shells. and other parameters; at the same time, it can efficiently calibrate the relationship between shell thickness-metal local shrinkage-temperature and interface heat transfer coefficient, which is highly scientific and professional. The above embodiment can also simulate the conditions and stress states of actual precision casting shells undergoing shrinkage stress bending after primary baking and secondary baking, thereby truly reflecting the stiffness of different shell thicknesses at different temperatures, and can provide precision casting solutions for precision castings. The process provides the basis for accurate shell stiffness and strength data. Embodiments of the present invention can be widely used in the field of precision casting, can provide accurate shell stiffness and strength data basis for the precision casting process, and can provide accurate data basis for precision castings, especially high-end large-scale thin-wall castings, such as turbine rear casings, diffusers and other castings. Deformation prediction and control, thermal cracking prediction and control, and collapse possibility prediction during the mold shell pouring process provide accurate data support quickly and efficiently.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above. Those skilled in the art can make various variations or modifications within the scope of the claims, which does not affect the essence of the present invention. The above preferred features can be used in any combination as long as they do not conflict with each other.

Claims (10)

1. A method for preparing a variable thickness casting mold, which is characterized in that it includes: Provide a stick sprue wax pattern; Provide a plurality of flake wax patterns, form a plurality of grooves at equal intervals along the length direction on the rod-shaped runner wax pattern, insert the flake wax patterns into the grooves and bond them to form a tree; According to the bottom-up order, starting from the first layer of flake wax mold, the step-by-step slurry and sand spraying process is carried out in sequence. The slurry position for each time or for a preset number of intervals is gradually raised by one tree group along the direction of the tree group. spacing, up to the last layer of flake wax pattern; Carry out uniform sealing treatment on the group of trees and dry them under blowing conditions; The tree is dewaxed to obtain a variable thickness cast. 2. The method for preparing a variable-thickness casting mold according to claim 1, characterized in that, starting from the first layer of flaky wax molds, a step-by-step slurry-dipping and sand-dipping process is performed in sequence, wherein: a slurry-dipping and sand-dipping process is carried out. It includes making the top layer, middle layer and back layer in sequence; after the preparation of each back layer, it is dried under blowing conditions. 3. The method for preparing a variable thickness casting mold according to claim 2, characterized in that for the silicon oxide type shell, after the preparation of each back layer is completed, it is dried under blowing conditions for 4-12 hours. 4. The method for preparing a variable thickness casting mold according to claim 2, characterized in that, for an alumina type shell, after the preparation of each back layer is completed, it is dried under blowing conditions for 8-16 hours. 5. The method for preparing a variable-thickness casting mold according to claim 1, characterized in that the tree assembly is dewaxed, wherein: dewaxing is performed at 150-200°C. 6. A variable thickness casting mold, characterized in that it is prepared by the method for preparing a variable thickness casting mold according to any one of claims 1 to 5. 7. A method for measuring the mechanical performance parameters of ceramic shells, which is characterized by including: After cutting and polishing the variable-thickness casting mold according to claim 6 along the root of the test piece, a molded shell test piece with different thicknesses is obtained; The molded shell test pieces are uniformly placed in a mold shell roasting furnace and roasted to simulate the one-time baking process of a real precision casting shell, and obtain molded shell test pieces with different numbers of back layers; Put the molded shell test pieces with different numbers of back layers into a three-point bending tester to simulate the secondary baking process of the molded shell. Conduct three-point bending tests on multiple shell test pieces with different thicknesses one by one to obtain the flow heat Mechanical property parameters of the casting mold in the solid coupling model. 8. A calibration method for interface heat transfer coefficient, which is characterized by including: Performing primary roasting and mold shell preheating on the variable thickness casting mold according to claim 6; Set a thermocouple on each shell test piece on the variable thickness casting mold; Transfer the variable thickness casting to the vacuum pouring furnace for pouring, and obtain the temperature-time data of the thermocouple during the pouring process; According to the temperature-time data, the interface heat transfer coefficient-time curve data at each shell test piece was back-calculated, and the mechanical property parameters of the casting mold were brought in. Combined with the numerical simulation method, the values of the shell test pieces with different thicknesses and Model the change of alloy-shell contact pressure and gap size with time at the interface of metal specimens with different alloy thicknesses, and establish a digital model of the change of interface heat transfer coefficient with time, interface gap and interface pressure. 9. The calibration method of interface heat transfer coefficient according to claim 8, characterized in that a thermocouple is provided on each shell test piece on the variable thickness casting mold, wherein: on the variable thickness casting mold A thermocouple is set at the center of each shell test piece using the punching method. 10. The calibration method of interface heat transfer coefficient according to claim 8 or 9, characterized in that the variable thickness casting mold is transferred to a vacuum pouring furnace for pouring, and the temperature-time of the thermocouple is obtained during the pouring process. After the data, it also includes: cutting the metal test piece to observe the microstructure of the metal test piece, and conducting tensile mechanical testing on the metal test piece.