CN107909189B - Shrinkage cavity defect prediction method for simulating aluminum alloy sand casting process - Google Patents

Shrinkage cavity defect prediction method for simulating aluminum alloy sand casting process Download PDF

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CN107909189B
CN107909189B CN201710983587.6A CN201710983587A CN107909189B CN 107909189 B CN107909189 B CN 107909189B CN 201710983587 A CN201710983587 A CN 201710983587A CN 107909189 B CN107909189 B CN 107909189B
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牛晓峰
刘一鸣
王宝健
阎佩雯
宋振亮
黄志伟
程伟丽
侯华
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Taiyuan University of Technology
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Abstract

The invention relates to a shrinkage cavity defect prediction method for simulating an aluminum alloy sand casting process, which aims at the shrinkage cavity defect in the aluminum alloy sand casting process, carries out simulation prediction before actual casting, and is beneficial to reducing casting defects in the actual casting; the prediction method has the advantages of few used equipment, universal and reasonable calculation method, high calculation speed and accurate simulation result, and is suitable for predicting shrinkage cavity defects in the sand casting of the aluminum alloy castings.

Description

Shrinkage cavity defect prediction method for simulating aluminum alloy sand casting process
Technical Field
The invention relates to a shrinkage cavity defect prediction method for simulating an aluminum alloy sand casting process, and belongs to the technical field of aluminum alloy sand casting process optimization and calculation.
Background
The aluminum alloy sand casting is a casting method for obtaining parts with expected shapes, sizes and performances after aluminum alloy metal liquid flows into a casting mould and is solidified; the process comprises the following steps: and the molten aluminum alloy flows into the cavity through the sprue, the sprue and the ingate in sequence to fill the whole cavity until the casting is completely cooled and solidified to obtain the expected casting.
Shrinkage cavities can be generated due to insufficient feeding in the shrinkage process when the molten aluminum alloy is solidified, and the formation of the shrinkage cavities causes casting defects and seriously affects the quality of castings; the formation of shrinkage cavities in the aluminum alloy molten metal solidification process is a complex process, the whole formation process is shown by a numerical simulation method, the distribution and the size of the shrinkage cavities formed in the aluminum alloy molten metal solidification process are accurately predicted, and a theoretical basis is provided for optimizing the process, designing and preventing a die and reducing casting defects.
Disclosure of Invention
Object of the Invention
The invention aims to solve the shrinkage cavity defect existing in the aluminum alloy sand casting process, show the forming process of the shrinkage cavity by establishing a mathematical model and program calculation according to the characteristics of the aluminum alloy sand casting solidification process, predict the distribution and the size of the shrinkage cavity formed in the solidification process of the dumbbell-shaped aluminum alloy casting, and provide a theoretical basis for optimizing the process and the mold design, and preventing and reducing the defect of the casting.
Technical scheme
(1) Obtaining the dumbbell-shaped casting of the aluminum alloy
Firstly, prefabricated sand casting mold
Preparing a dumbbell-shaped wood model and forming; polishing the surface of the wood mold by using abrasive paper to make the surface smooth; taking a dumbbell-shaped wood mold as a forming model, manufacturing a sand mold by using furan resin sand, and arranging a zirconium oxide filter screen gate at a gate of the sand mold for later use;
smelting molten aluminium alloy
Weighing 5kg +/-0.1 kg of aluminum alloy, placing the aluminum alloy in a melting crucible, heating to 720 +/-2 ℃, stirring the molten liquid, degassing by using hexachloroethane, removing slag, and standing for 5 min; the temperature of the molten aluminum alloy is reduced to 690 +/-2 ℃ for later use;
③ Sand casting
Injecting molten aluminum alloy into a pouring gate of a sand mold, and allowing molten metal to enter a mold cavity and fill the mold cavity;
cooling and taking out the casting
After casting, placing the mould and the casting in the mould in natural air to be cooled to 25 ℃; cooling, opening the mold, and taking out the dumbbell-shaped casting;
fifthly, cleaning the surface of the casting
Cleaning the surface of the casting by using a metal brush, mechanically cutting off the residual head of the casting, and polishing the surface of the casting by using abrasive paper to clean the surface and form the dumbbell-shaped casting;
(2) establishing a shrinkage cavity defect prediction model
Firstly, establishing three-dimensional model, dispersing particles and initializing
Firstly, establishing a three-dimensional entity by utilizing modeling software, then carrying out particle dispersion on aluminum alloy melt in a casting mold and a cavity, and setting initial attributes of particles, wherein the method comprises the following specific steps:
1) building of three-dimensional entities
Establishing a three-dimensional model of the aluminum alloy melt in the casting mold and the cavity by using three-dimensional modeling software;
2) dispersing particles and setting initial parameters of particles
Three-dimensional modeling software derives a three-dimensional entity, and the initial position of the particle is determined through particle dispersion; setting initial pressure, density, viscosity, initial temperature, heat conductivity coefficient and specific heat capacity of particles with different attributes according to different types of the particles; determining time step length and initial smooth length value, and defining every 5000 time step lengths as a calculation stage; the casting mould particles are solid wall boundary particles, and the boundary is processed by adopting a repulsive force method;
searching method for building linked list
The method comprises the following steps of determining particles interacting in an influence domain by dividing a problem domain into small regions, realizing particle pairing and storing particle pair information, and specifically comprising the following steps:
1) partitioning problem domains into regions
Dividing all particles into regions according to the initial positions of the particles, wherein each particle belongs to a specific region, and only searching the particles in the region where the particles are located and the surrounding region in the particle searching process after dividing the regions;
2) particle search, pairing, and storing particle pair information
In the region where only the particles are searchedAnd under the condition of the particles in the surrounding area, the spherical area with the position of the particle i as the center of a circle and 2 times of smooth length as the radius represents the influence area of the particle i; when the distance r between the particle i and the particle jijWhen the value of (d) is less than or equal to 2 times of the smooth length, it can be considered that the particle i is matched with the particle j, and the influence of the particle j on the particle i is considered in the subsequent calculation; under the condition of meeting the matching condition, in order to avoid repeated matching, matching is completed and the particle pair information is stored only when the searched j particle number is smaller than the i particle number;
after the calculation of each time step is completed, carrying out the region division, the search, the pairing and the storage of the particle pair information again;
calculating the temperature and acceleration of the particles
The temperature of the aluminum alloy molten metal particles is reduced, the temperature change can affect the physical property parameters of the molten metal particles, and the physical property parameter processing is realized based on the condition; besides considering the temperature change, the latent heat treatment of crystallization in the solidification process is also key, and the specific steps are as follows:
1) calculating temperature and processing physical parameters;
the particle temperature calculation and physical property parameter processing method comprises the following specific steps:
and calculating the temperature change of all the particles, wherein the specific expression is as follows:
Figure BDA0001439987570000031
in the formula:
Figure BDA0001439987570000032
denotes the rate of change of i particle temperature with time, CiDenotes the i-particle specific heat capacity, ρ i denotes the i-particle density,
Figure BDA0001439987570000033
representing the sum of the influence of j particles on i particles in the influence domain, N representing the number of particles in the influence domain, mjDenotes the mass, ρ, of the particle jjDenotes the density of j particles，λiDenotes the thermal conductivity of i particle, λjDenotes the thermal conductivity, T, of j particlesiDenotes the temperature value, T, of the i particlesjDenotes the temperature value of j particles, rijRepresents the distance between the i and j particles,
Figure BDA0001439987570000034
expressing smooth function gradient, adopting an index method to express, and expressing coordinate directions by Greek letter superscripts alpha and beta;
for the particles in the cavity, the viscosity, the thermal conductivity coefficient and the density change along with the change of temperature in the calculation process, and the specific expression is as follows:
the viscosity changes with temperature, and the specific relation is as follows:
when the particle temperature is 536-574 deg.C, eta is 0.024T2-28T +8164.656, η in pa · s; when the temperature of the particles is 574-576 ℃, eta is 11.56-0.02T, and eta is pa · s; when the temperature of the particles is 576-589 ℃, eta is 1.013-0.00169T, and eta is pa · s; when the temperature of the particles is 589-720 ℃, eta is 0.0118, and eta is pa · s; η represents the particle viscosity, T represents the particle temperature, in units;
the specific relation of the change of the thermal conductivity coefficient along with the temperature is as follows:
when the particle temperature is less than 536 ℃, λ is 170, λ is W/(m ℃); when the particle temperature is 536-589 deg.c, lambda is 1081.2-1.7T, and lambda is W/(m deg.c); when the particle temperature is 589-720 ℃, lambda is 80, and lambda is W/(m DEG C);
the density changes with the temperature between different calculation stages, and the specific relation is as follows:
when the temperature of the particles is less than 536 ℃, rho is 2702, and the rho unit is kg/m3(ii) a When the temperature of the particles is 536-589 ℃, rho is 4336.8-3.05T, and the rho unit is kg/m3(ii) a When the temperature of the particles is 589-720 ℃, rho is 2540, and the unit of rho is kg/m3；
2) Calculating the acceleration of the metal liquid particles;
Figure BDA0001439987570000041
Figure BDA0001439987570000042
in the formula: w denotes a smoothing function, αdTake value as a constant
Figure BDA0001439987570000043
Figure BDA0001439987570000044
Representing the sum of the influence of j particles on i particles in the influence domain, N representing the number of particles in the influence domain, mjDenotes the mass, p, of the particle jiDenotes the pressure value, p, of the particle ijDenotes the pressure value, ρ, of the particle jiDenotes the density, ρ, of the particle ijRepresents a particle j
Figure BDA0001439987570000051
Representing the speed difference of the particles i and the particles j by an index method, wherein Greek letters are marked with alpha and beta to represent coordinate directions, and R represents the ratio of the distance between the particles to the smooth length;
the calculation of the above equation requires the calculation of a particle pressure value p, which is expressed as follows:
Figure BDA0001439987570000052
Figure BDA0001439987570000053
in the formula: p is a radical of0Denotes the initial value of the pressure, p0Representing the initial density of particles, gamma is a constant, g represents the acceleration of gravity, and H represents the height of the casting;
in the same calculation stage, the density change rate is obtained by the following formula, and the specific expression is as follows:
Figure BDA0001439987570000054
in the formula:
Figure BDA0001439987570000055
representing the rate of change of the particle i density over time,
Figure BDA0001439987570000056
represents the sum of the influence of j particles on i particles in the influence domain, N represents the number of particles in the influence domain, mjWhich represents the mass of the particle j,
Figure BDA0001439987570000057
representing the speed difference between the particle i and the particle j by adopting an index method, and indicating coordinate directions by Greek letter superscripts alpha and beta;
3) latent heat treatment
Latent heat treatment is a factor which must be considered in the solidification process, the influence of latent heat release on temperature calculation is reflected by adopting a method of correcting a proportional heat capacity value, and when the temperature value of the molten metal particles is between a liquidus and a solidus, the corrected specific heat capacity CeThe calculation formula is as follows:
Figure BDA0001439987570000058
in the formula: ceDenotes the corrected specific heat capacity, CPDenotes the original specific heat capacity, LfRepresents the latent heat of solidification, T, of the molten metalSRepresents the solidus temperature, TlRepresents the liquidus temperature;
original specific heat capacity CPThe specific relation with the change of the temperature is as follows:
when the particle temperature is less than or equal to 536 ℃, Cp＝0.0006T+0.82，CpThe unit KJ/(kg. DEG C.); when the particle temperature is 536-720 ℃, Cp＝1.14，CpThe unit is KJ/(kg. DEG C); t represents the particle temperature in units;
fourthly, updating the temperature, the speed and the position of the particles through a time step, and the method comprises the following specific steps:
1) the temperature value of the particle at the current moment is equal to the temperature value at the previous moment plus the change rate of the temperature along with the time multiplied by the time step;
2) the metal liquid particle velocity and position are updated as follows:
the speed value of the metal liquid particle at the current moment is equal to the speed value of the previous moment plus the acceleration multiplied by the time step; the position value of the metal liquid particle at the current moment is equal to the position value of the previous moment, plus the acceleration multiplied by the square of the time step and then multiplied by
Figure BDA0001439987570000061
After one time step is calculated, carrying out region division, searching and pairing on the particles and calculating the temperature, the speed, the position and the physical property parameters of the particles again until the calculation is finished;
the shrinkage cavity defect prediction method in the aluminum alloy sand casting process is completed by a computer program, and the program is compiled by taking VC + + as an open platform, wherein the computer program is as follows:
Figure RE-RE-RE-GDA0003224954020000011
Figure RE-RE-RE-GDA0003224954020000021
Figure RE-RE-RE-GDA0003224954020000031
Figure RE-RE-RE-GDA0003224954020000041
(3) predicted results
The total number of the particles in the calculation is 144000, the numerical simulation result shows that shrinkage cavities appear in the dumbbell-shaped casting, and the numerical simulation result is consistent with the actual measurement result.
Has the advantages that:
compared with the background technology, the method has obvious advancement, aims at the shrinkage cavity defect phenomenon existing in the aluminum alloy sand casting process, carries out simulation prediction before actual casting, and is beneficial to reducing casting defects in the actual casting; writing a program by taking VC + + as a development platform, carrying out computer operation to obtain a prediction result, and displaying the distribution condition and the size of shrinkage cavity defects in sand casting of aluminum alloy castings; the prediction method has the advantages of less used equipment, universal and reasonable calculation method, high calculation speed and accurate simulation result, is suitable for predicting the shrinkage cavity defect under the sand casting of the aluminum alloy casting, can also be used for predicting the sand casting defect of other ferrous metals, and provides a guidance basis for optimizing the casting process and avoiding and reducing the shrinkage cavity defect of the casting.
Drawings
FIG. 1 is a front view of an aluminum alloy dumbbell casting
FIG. 2 is a plan view of an aluminum alloy dumbbell casting
FIG. 3 is a side view of an aluminum alloy dumbbell casting
FIG. 4 is a state diagram of sand casting of aluminum alloy dumbbell castings
As shown in the figures, the list of reference numbers is as follows:
1. the dumbbell comprises an upper dumbbell body, 2 a lower dumbbell body, 3 a neck, 4 a steel die sleeve, 5 a sand mold die, 6 an upper dumbbell cavity, 7 a lower dumbbell cavity, 8 a neck cavity, 9 a zirconium oxide pouring gate, 10 aluminum alloy liquid, 11 a first opening and closing frame, 12 a second opening and closing frame, 13 a third opening and closing frame, 14 a fourth opening and closing frame.
Detailed Description
The invention is further described below with reference to the accompanying drawings:
fig. 1, 2 and 3 show the structure of an aluminum alloy dumbbell casting, wherein the upper part of the aluminum alloy dumbbell is an upper dumbbell 1, the lower part of the aluminum alloy dumbbell is a lower dumbbell 2, and the middle part of the aluminum alloy dumbbell is connected into a whole by a neck part 3 and is in a dumbbell shape.
FIG. 4 shows a state diagram of sand casting of dumbbell-shaped aluminum alloy castings, in which the positions and connection relationships of the parts are correct and the installation is firm; the exterior of a sand mold 5 used for sand mold casting is fixed by a steel mold sleeve 4, and the steel mold sleeve 4 is connected and fixed by a first opening and closing frame 11, a second opening and closing frame 12, a third opening and closing frame 13 and a fourth opening and closing frame 14; the upper part of the steel die sleeve 4 is provided with a zirconia sprue 9; an upper dumbbell-shaped cavity 6 is arranged at the inner upper part of the sand mold 5, the lower part of the upper dumbbell-shaped cavity 6 is connected with a neck cavity 8, and the lower part of the neck cavity 8 is connected with a lower dumbbell-shaped cavity 7; the upper part of the upper dumbbell-shaped cavity 6 is connected with a zirconia gate 9; aluminum alloy liquid 10 is filled in the upper dumbbell-shaped cavity 6, the neck cavity 8 and the lower dumbbell-shaped cavity 7.

Claims (2)

1. A shrinkage cavity defect prediction method for simulating an aluminum alloy sand casting process is characterized by comprising the following steps of:
(1) obtaining the dumbbell-shaped casting of the aluminum alloy
Firstly, prefabricated sand casting mold
Preparing a dumbbell-shaped wood model and forming; polishing the surface of the wood mold by using abrasive paper to make the surface smooth; taking a dumbbell-shaped wood mold as a forming model, manufacturing a sand mold by using furan resin sand, and arranging a zirconia filter screen pouring gate at the pouring gate of the sand mold for later use;
melting molten aluminum alloy
Weighing 5kg +/-0.1 kg of aluminum alloy, placing the aluminum alloy in a melting crucible, heating to 720 +/-2 ℃, stirring the melt, degassing by using hexachloroethane, removing slag, and standing for 5 min; the temperature of the molten aluminum alloy is reduced to 690 +/-2 ℃ for later use;
③ Sand casting
Injecting molten aluminum alloy into a pouring gate of a sand mold, and allowing molten metal to enter a mold cavity and fill the mold cavity;
cooling and taking out the casting
After casting, placing the mould and the casting in the mould in natural air to be cooled to 25 ℃; cooling, opening the mold, and taking out the dumbbell-shaped casting;
fifthly, cleaning the surface of the casting
Cleaning the surface of the casting by using a metal brush, mechanically cutting off the residual head of the casting, and polishing the surface of the casting by using abrasive paper to clean the surface and form the dumbbell-shaped casting;
(2) establishing a shrinkage cavity defect prediction model
Firstly, establishing three-dimensional model, dispersing particles and initializing
Firstly, establishing a three-dimensional entity by utilizing modeling software, then carrying out particle dispersion on aluminum alloy melt in a casting mold and a cavity, and setting initial attributes of particles, wherein the method comprises the following specific steps:
1) building of three-dimensional entities
Establishing a three-dimensional model of the aluminum alloy melt in the casting mold and the cavity by using three-dimensional modeling software;
2) dispersing particles and setting initial parameters of particles
Three-dimensional modeling software derives a three-dimensional entity, and the initial position of the particle is determined through particle dispersion; setting initial pressure, density, viscosity, initial temperature, heat conductivity coefficient and specific heat capacity of particles with different attributes according to different types of the particles; determining time step length and initial smooth length value, and defining every 5000 time step lengths as a calculation stage; the casting mould particles are solid wall boundary particles, and the boundary is processed by adopting a repulsive force method;
searching method for building linked list
The method comprises the following steps of determining particles interacting in an influence domain by dividing a problem domain into small regions, realizing particle pairing and storing particle pair information, and specifically comprising the following steps:
1) partitioning problem domains into regions
Dividing all particles into regions according to the initial positions of the particles, wherein each particle belongs to a specific region, and only searching the particles in the region where the particle is located and the surrounding region in the particle searching process after dividing the regions;
2) particle search, pairing, and storing particle pair information
Under the condition of only searching particles in the region where the particles are located and the surrounding region, a spherical region with the position where the particle i is located as the center of a circle and 2 times of smooth length as the radius represents the influence domain of the particle i; when the distance r between the particle i and the particle jijWhen the value of (d) is less than or equal to 2 times of the smooth length, it can be considered that the particle i is matched with the particle j, and the influence of the particle j on the particle i is considered in the subsequent calculation; under the condition of meeting the matching condition, only the repeated pairing is avoidedCompleting pairing and storing the particle pair information when the searched j particle number is smaller than the i particle number;
after the calculation of each time step is completed, carrying out the region division, the search, the pairing and the storage of the particle pair information again;
calculating the temperature and acceleration of the particles
The temperature of the aluminum alloy molten metal particles is reduced, the temperature change can affect the physical property parameters of the molten metal particles, and the physical property parameter processing is realized based on the condition; besides considering the temperature change, the latent heat treatment of crystallization in the solidification process is also key, and the specific steps are as follows:
1) calculating temperature and processing physical parameters;
the particle temperature calculation and physical property parameter processing method comprises the following specific steps:
and calculating the temperature change of all the particles, wherein the specific expression is as follows:
Figure FDA0001439987560000021
in the formula:
Figure FDA0001439987560000022
denotes the rate of change of i particle temperature with time, CiDenotes the i particle specific heat capacity, ρiThe density of the particles is expressed as i,
Figure FDA0001439987560000031
representing the sum of the influence of j particles on i particles in the influence domain, N representing the number of particles in the influence domain, mjDenotes the mass, ρ, of the particle jjDenotes the density of j particles, λiDenotes the thermal conductivity of i particles, λjDenotes the thermal conductivity, T, of j particlesiDenotes the temperature value, T, of the i particlesjDenotes the temperature value of j particles, rijRepresents the distance between the i and j particles,
Figure FDA0001439987560000032
expressing the smooth function gradient by adopting an index method, and expressing the coordinate directions by using Greek letter superscripts alpha and beta;
for the particles in the cavity, the viscosity, the thermal conductivity coefficient and the density change along with the change of temperature in the calculation process, and the specific expression is as follows:
the viscosity changes with temperature, and the specific relation is as follows:
when the particle temperature is 536-574 deg.C, eta is 0.024T2-28T +8164.656, η in pa · s; when the temperature of the particles is 574-576 ℃, eta is 11.56-0.02T, and eta is pa · s; when the temperature of the particles is 576-589 ℃, eta is 1.013-0.00169T, and eta is pa · s; when the temperature of the particles is 589-720 ℃, eta is 0.0118, and eta is pa · s; η represents the particle viscosity, T represents the particle temperature, in units;
the specific relation of the change of the thermal conductivity coefficient along with the temperature is as follows:
when the particle temperature is less than 536 ℃, λ is 170, λ is W/(m ℃); when the particle temperature is 536-589 deg.c, lambda is 1081.2-1.7T, and lambda is W/(m deg.c); when the particle temperature is 589-720 ℃, lambda is 80, and lambda is W/(m DEG C);
the density changes with the temperature between different calculation stages, and the specific relation is as follows:
when the temperature of the particles is less than 536 ℃, rho is 2702, and the rho unit is kg/m3(ii) a When the temperature of the particles is 536-589 ℃, rho is 4336.8-3.05T, and the rho unit is kg/m3(ii) a When the temperature of the particles is 589-720 ℃, rho is 2540, and the unit of rho is kg/m3；
2) Calculating the acceleration of the metal liquid particles;
Figure FDA0001439987560000041
Figure FDA0001439987560000042
in the formula: w denotes a smoothing function, αdTake value as a constant
Figure FDA0001439987560000043
Figure FDA0001439987560000044
Representing the sum of the influence of j particles on i particles in the influence domain, N representing the number of particles in the influence domain, mjDenotes the mass, p, of the particle jiDenotes the pressure value, p, of the particle ijDenotes the pressure value, ρ, of the particle jiDenotes the density, ρ, of the particle ijDenotes the density of the particle j, g denotes the acceleration of gravity of the particle, ηiAnd ηjRespectively representing kinetic viscosity coefficients of the particles i and the particles j,
Figure FDA0001439987560000045
representing the speed difference of the particles i and the particles j by an index method, wherein Greek letters are marked with alpha and beta to represent coordinate directions, and R represents the ratio of the distance between the particles to the smooth length;
the calculation of the above equation requires the calculation of a particle pressure value p, which is expressed as follows:
Figure FDA0001439987560000046
Figure FDA0001439987560000047
in the formula: p is a radical of0Denotes the initial value of the pressure, p0Representing the initial density of particles, gamma is a constant, g represents the acceleration of gravity, and H represents the height of the casting;
in the same calculation stage, the density change rate is obtained by the following formula, and the specific expression is as follows:
Figure FDA0001439987560000048
in the formula:
Figure FDA0001439987560000049
representing the rate of change of the particle i density over time,
Figure FDA00014399875600000410
representing the sum of the influence of j particles on i particles in the influence domain, N representing the number of particles in the influence domain, mjWhich represents the mass of the particle j,
Figure FDA00014399875600000411
representing the speed difference between the particle i and the particle j by adopting an index method, and indicating coordinate directions by Greek letter superscripts alpha and beta;
3) latent heat treatment
Latent heat treatment is a factor which must be considered in the solidification process, the influence of latent heat release on temperature calculation is embodied by adopting a method of correcting a proportional heat capacity value, and when the temperature value of the molten metal particles is between a liquidus and a solidus, the corrected specific heat capacity CeThe calculation formula is as follows:
Figure FDA0001439987560000051
in the formula: ceDenotes the corrected specific heat capacity, CPDenotes the original specific heat capacity, LfRepresents the latent heat of solidification, T, of the molten metalSRepresents the solidus temperature, TlRepresents the liquidus temperature;
original specific heat capacity CPThe specific relation with the change of the temperature is as follows:
when the particle temperature is less than or equal to 536 ℃, Cp＝0.0006T+0.82，CpThe unit KJ/(kg. DEG C.); when the particle temperature is 536-720 ℃, Cp＝1.14，CpThe unit is KJ/(kg. DEG C); t represents the particle temperature in units;
fourthly, updating the temperature, the speed and the position of the particles through a time step, and the method comprises the following specific steps:
1) the temperature value of the particle at the current moment is equal to the temperature value at the previous moment plus the change rate of the temperature along with the time multiplied by the time step;
2) the metal liquid particle velocity and position are updated as follows:
the speed value of the metal liquid particle at the current moment is equal to the speed value of the previous moment plus the acceleration multiplied by the time step; the position value of the metal liquid particle at the current moment is equal to the position value of the previous moment, the acceleration is multiplied by the square of the time step and then multiplied by
Figure FDA0001439987560000052
After one time step is calculated, carrying out region division, searching and pairing on the particles and calculating the temperature, the speed, the position and the physical property parameters of the particles again until the calculation is finished;
the shrinkage cavity defect prediction method in the aluminum alloy sand casting process is completed by a computer program, and the program is compiled by taking VC + + as a development platform;
(3) predicted results
The total number of the particles in the calculation is 144000, the numerical simulation result shows that shrinkage cavities appear in the dumbbell-shaped casting, and the numerical simulation result is consistent with the actual measurement result.
2. The method for predicting the shrinkage cavity defect in the process of simulating the sand casting of the aluminum alloy according to claim 1, which is characterized by comprising the following steps of: the exterior of a sand mold (5) used for sand mold casting is fixed by a steel mold sleeve (4), and the steel mold sleeve (4) is connected and fixed by a first opening and closing frame (11), a second opening and closing frame (12), a third opening and closing frame (13) and a fourth opening and closing frame (14); the upper part of the steel die sleeve (4) is provided with a zirconia sprue (9); an upper dumbbell-shaped cavity (6) is arranged at the inner upper part of the sand mold (5), the lower part of the upper dumbbell-shaped cavity (6) is connected with a neck cavity (8), and the lower part of the neck cavity (8) is connected with a lower dumbbell-shaped cavity (7); the upper part of the upper dumbbell-shaped cavity (6) is connected with a zirconium oxide sprue (9); aluminum alloy liquid (10) is filled in the upper dumbbell cavity (6), the neck cavity (8) and the lower dumbbell cavity (7).
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