CN109909413B - Forging die speed curve iteration optimization method based on hot working diagram - Google Patents
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Abstract
The invention discloses a forging die speed curve iteration optimization method based on a hot working diagram, which comprises the following specific steps: importing an analysis model in finite element software and setting boundary conditions; calling a finite element program integrating the forging die speed curve optimization function to carry out finite elementSimulating; and obtaining an optimized forging die speed curve. The realization process of the forging die speed curve optimization function comprises the following steps: firstly, setting the initial temperature T of the forge piece0Initial strain0Starting to enter an iterative loop; at the moment t, equally dividing the speed range allowed by the press or equally dividing the logarithm into 2-10 parts, calculating the dissipation coefficient and the instability coefficient, and calculating the average dissipation coefficient of the forge piece; selecting a pressing speed V with an average dissipation coefficient of 35-45% and no instability pointtAs the optimum speed; finally store VtAnd will VtPerforming simulation calculation as the pressing speed of the next time step; and the process is circulated until the forging die finishes the whole travel, and a forging die speed curve is output. The invention can better improve the forming performance of the material and improve the microstructure of the forging.
Description
Technical Field
The invention relates to the field of metal hot forging, in particular to a forging die speed curve iteration optimization method based on a hot working diagram.
Background
The hot working diagram reflects the distribution and evolution rules of the energy dissipation coefficient and the instability coefficient of the metal under different deformation temperatures, strain rates and strains, and can be generally divided into a dynamic recrystallization region, an incomplete dynamic recrystallization region, a deformation instability region and the like according to the difference of the microstructure evolution rule and the deformation mechanism, so that when forging process parameters are set, whether the hot forging process parameters are reasonable or not is judged according to the region where the hot working parameters fall. In the hot forging, the strain rate of the forge piece in the deformation process can be controlled by selecting a reasonable forging die speed curve, so that the region where hot working parameters fall is changed, and the effect of optimizing the microstructure of the forge piece is achieved.
At present, there are patents that propose the optimization of process parameters by applying a hot working drawing to hot deformation.
The Chinese patent of invention (application number: 201510897211.4) discloses a method for determining hot extrusion process parameters of nickel-base superalloy, and the hot extrusion process of powder nickel-base superalloy is determined through hot compression experiments and finite element simulation.
The Chinese patent of invention (application number: 201511025177.8) discloses a method for making a hot working process of a high-temperature alloy GH984G18, which can avoid the defects of coarse crystals, mixed crystals, cracks and the like after hot working.
The Chinese invention patent (application number: 201710190026.0) discloses a cylindrical piece hot-spinning/performance integrated control method based on a hot-working diagram, and optimizes the forming temperature and the strain rate in the cylindrical piece hot-spinning.
The Chinese invention patent (application number: 201711265241.9) discloses a method for optimizing the hot working process of aluminum alloy by a hot working diagram, so as to improve the processing performance of the aluminum alloy in hot working.
The Chinese invention patent (application number: 201810360313.6) discloses a method for determining the evolution mechanism and the hot working performance of the hot deformation structure of C-Mn-Al high-strength steel, thereby guiding the formulation of the hot working process of the high-strength steel.
Chinese invention patent (application number: 201810407510.9) discloses a 300M steel forging process parameter optimization method based on instability analysis, wherein grain size is introduced into a hot working drawing, and the optimal process parameters of 300M steel forging are determined.
The methods all have the common point that the deformation speed or the strain rate is optimized as a fixed value, and the optimal deformation speed is input into a forging press for forging. However, in the hot forging of metals, the speed or strain rate of different parts of the forging is not a constant value, but a curve which changes with time or displacement and changes with time. Moreover, more and more deformation processes are carried out on forging equipment with the function of setting a complex speed curve, and the constant forging speed is not beneficial to fully exerting the forming performance of the forging. According to a method for automatically drawing a hot working drawing of a material disclosed in the chinese invention patent (application No. 200610134755.6), the hot working drawing and the optimal hot working parameters are significantly changed with the increase of time or displacement.
Therefore, by setting the optimized forging die speed curve, the forming performance of the forging piece can be further improved. In metal hot forging, the characteristic that the strain rate changes constantly needs to be considered, an optimal forging die speed curve is made according to a hot working diagram of hot metal, the hot working performance of materials is improved, and an optimal forging piece microstructure is obtained. However, in the aspect of establishing an optimal forging die speed curve according to a metal hot working diagram, domestic and foreign research is still blank, which greatly limits further improvement of material processing performance in a hot forging process and hinders progress of the forging production technology in China.
Disclosure of Invention
In order to solve the problems, the invention provides a forging die speed curve iteration optimization method based on a hot working diagram, which aims to overcome the defect that the existing forging die speed curve cannot be determined according to the hot working diagram.
The invention conception is as follows: by integrating the hot working diagram into the finite element simulation, the optimal speed of the forging die is selected according to the hot working diagram at each simulation time step, and the speed of the forging die is iteratively optimized in the whole process of pressing down the forging die to obtain a speed curve of the forging die, so that the microstructure of the forging piece is optimized.
Therefore, the technical scheme of the invention is as follows: a forging die speed curve iteration optimization method based on a hot working diagram comprises a stress-strain curve obtained through a hot compression experiment and a generated hot working diagram, and is characterized by comprising the following specific steps:
(1) importing an analysis model in finite element software and setting boundary conditions;
(2) calling a finite element program integrating the forging die speed curve optimization function to carry out finite element simulation;
(3) obtaining an optimized forging die speed curve;
wherein, the forging die speed curve optimization function in the step (2) needs to be realized by secondary development of a finite element program, and the specific flow is as follows:
firstly, setting the initial temperature T of the forge piece0Initial strain0Starting to enter an iterative loop;
at the moment t, equally dividing the speed range allowed by the press or equally dividing the logarithm into 2-10 parts, respectively calculating the dissipation coefficient and the instability coefficient of the forge piece at different pressing speeds, and calculating the average dissipation coefficient of the forge piece;
then, the pressing speed V with the average dissipation coefficient of 35-45% and no instability point is selectedtAs the optimum speed;
finally, V is storedtAnd will VtPerforming simulation calculation as the pressing speed of the next time step;
and circulating the steps until the forging die finishes the whole stroke, and outputting a forging die speed curve through a finite element program interface.
Preferably, the range of speeds allowed by the press is divided equally into 10 parts, or after taking the number of pairs.
Preferably, the depression speed with the average dissipation factor closest to 40% is selected as the optimal depression speed at time t.
Preferably, the process of optimizing the speed profile is applied to extrusion or heading processes as well as forging die processes.
Has the advantages that: compared with the conventional method, the forging die speed curve optimization method overcomes the defect that the current forging die speed curve can not be determined according to a hot working diagram; compared with other methods, the method is more efficient and accurate, and the forging die speed curve can be automatically obtained through optimization according to the hot working diagram. The method can better improve the forming performance of the material and improve the microstructure of the forging.
In the method, the speed range allowed by the press is divided into 10 parts by equal parts (or divided into equal parts after logarithm taking), so that the optimization speed can be improved while the calculation accuracy is ensured.
In the method, the average dissipation coefficient is selected to be 35-45% because for general metals, 35-45% is a dynamic recrystallization region, and the structure is ideal; and the pressing speed closest to 40% is selected as the optimal pressing speed, so that not only can the thermal processing parameters be ensured to fall in the dynamic recrystallization region, but also the optimal microstructure can be obtained.
Drawings
FIG. 1 is the iterative optimization process of the forging die speed curve in the invention.
FIG. 2 is a stress-strain plot of the present invention using 300M steel. Wherein:
FIG. 2 (a) shows that the strain rate of 300M steel is 0.01s at different deformation temperatures (900 ℃ C.) (1150 ℃ C.), different strains (0-0.9) and different strain rates-1Stress strain curve of (a);
FIG. 2 (b) shows that the strain rate of 300M steel is 0.1 s at different deformation temperatures (900 ℃ C.) (1150 ℃ C.), different strains (0-0.9) and different strain rates-1Stress strain curve of (a);
FIG. 2 (C) shows that the strain rate of 300M steel is 1s at different deformation temperatures (900 ℃ C.) (1150 ℃ C.), different strains (0-0.9) and-1stress strain curve of (a);
FIG. 2 (d) shows that the strain rate of 300M steel is 10s at different deformation temperatures (900 ℃ C.) (1150 ℃ C.), different strains (0-0.9) and different strain rates-1Stress strain curve of (a).
FIG. 3 is a hot working drawing of the present invention using 300M steel. Wherein:
FIG. 3 (a) shows that the present invention uses 300M steel at different deformation temperatures (900 ℃ C. and 1150 ℃ C.) and different strain rates (0.01-10 s)-1) A hot working pattern when the strain is 0.2;
FIG. 3 (b) is a graph showing that 300M steel is adopted in the present invention at different deformation temperatures (900 ℃ C. and 1150 ℃ C.) and different strain rates (0.01-10 s)-1) A hot working pattern when the strain is 0.4;
FIG. 3 (C) shows that the present invention uses 300M steel at different deformation temperatures (900 ℃ C. and 1150 ℃ C.) and different strain rates (0.01-10 s)-1) Strain, strainA hot working pattern at 0.6;
FIG. 3 (d) is a graph showing that 300M steel is adopted in the present invention at different deformation temperatures (900 ℃ C. and 1150 ℃ C.) and different strain rates (0.01-10 s)-1) And a thermal processing pattern when the strain was 0.8.
FIG. 4 is a graph of the 300M steel cylinder compression destabilization zone calculated using the present invention.
Figure 5 is a plot of the velocity of the compression head of a 300M steel cylinder optimized using the present invention.
Detailed Description
The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings, but the embodiment should not be construed as limiting the present invention.
The invention is shown in fig. 1 to 5:
the following describes a specific application of the optimization of the head speed curve in the compression process of a 300M steel cylinder sample, with reference to an example, and the specific implementation steps are as follows:
1. different deformation temperatures (900--1) And thermal compression experiments with different strains (0-0.9) are carried out, flow stress and strain data of a 300M steel cylinder sample during high-temperature plastic deformation are obtained, and a stress-strain curve as shown in figure 2 is drawn.
2. Fitting the obtained stress-strain data through Arrhenius model parameters (refer to the specific fitting method): octongning, huangliang, li jian jun, etc.; 300M high-temperature rheological behavior of high-strength steel and constitutive equation [ J ]. Zhongnan university Committee (Nature science edition), 2017(06):33-41, namely, a stress-strain relationship model of the 300M steel can be obtained as follows:
wherein σ p is the peak stress, in MPa;
is the strain rate, in units of s-1(ii) a R is the universal gas constant, R = 8.314J/(mol · K); t is the deformation temperature, in K; z is the temperature compensation strain rate and is calculated by the formula:
wherein the content of the first and second substances,
= 364.744 kJ/mol。
3. calculating a dissipation coefficient (eta) and a destabilization coefficient (zeta) in the hot working diagram, wherein the expressions are respectively as follows:
wherein σ is the flow stress, in MPa;
is the strain rate, in units of s-1∂ is the partial differential sign; the hot working map according to the above formula is shown in fig. 3.
4. The secondary development is carried out in DEFORM, and the forging die speed curve optimization function is integrated into a simulation program. The forging die speed curve optimization function integration steps are as follows:
1) reading initial temperature T of cell node0Initial strain0。
2) The allowable speed range of the press (0.01-10 s)-1) Taking the logarithm, equally dividing into 6 parts, and respectively dividing into 0.01s-1、0.03 s-1、0.1 s-1、0.32 s-1、1.00 s-1、3.16 s-1、10 s-1。
3) And (3) respectively calculating the eta and zeta values of the forge piece at different pressing speeds by using the expression in the step 3, and calculating the average value of the dissipation coefficient eta of the forge piece.
4) The depression velocity Vt with the average dissipation factor closest to 40% and without a buckling point is selected as the optimum velocity.
5) Store VtAnd will VtAs the depression speed for the next time step.
6) Judging whether the forging die movement is finished or not, if not, circularly and iteratively updating the temperature T of the forging pieceiAnd strainiJumping to step 2); if so, jumping to step 5.
7) And circulating the steps until the forging die finishes the whole stroke, and outputting a forging die speed curve through a finite element program interface.
5. The compression process of the cylindrical sample was simulated using a second developed program, the compression destabilization zone being shown in fig. 4.
6. The optimization result of the pressure head speed is obtained, and the optimized 300M steel cylinder compression pressure head speed curve is shown in figure 5. Therefore, a speed curve changing along with displacement is obtained, the speed of the forging die is a certain value, and the obtained speed curve of the forging die is more beneficial to improving the forming performance of the forging piece.
According to the technical scheme, the forging can be in a more complex shape, such as an aircraft landing gear, a turbine disc and the like, and the material can be made of 300M steel and also can be made of high-temperature alloy, aluminum alloy and other metals.
In the present invention, the method for obtaining the speed curve of the forging die can also be used for obtaining the equal time interval displacement curve of the forging die.
In the present invention, the process of optimizing the speed profile also includes extrusion, upsetting, and the like, which can optimize the speed profile using a hot working drawing.
Those skilled in the art will appreciate that the details of the present invention are not described in detail herein.
From the above description of the processing method, it should be understood by those skilled in the art that the present invention is not limited to the above-described embodiments, and modifications and substitutions based on the known technology in the art are within the scope of the present invention, which should be defined by the claims.
Claims (4)
1. A forging die speed curve iteration optimization method based on a hot working diagram comprises a stress-strain curve obtained through a hot compression experiment and a generated hot working diagram, and is characterized by comprising the following specific steps:
(1) importing an analysis model in finite element software and setting boundary conditions;
(2) calling a finite element program integrating the forging die speed curve optimization function to carry out finite element simulation;
(3) obtaining an optimized forging die speed curve;
wherein, the forging die speed curve optimization function in the step (2) needs to be realized by secondary development of a finite element program, and the specific flow is as follows:
firstly, setting the initial temperature T of the forge piece0Initial strain0Starting to enter an iterative loop;
at the moment t, equally dividing the speed range allowed by the press or equally dividing the logarithm into 2-10 parts, respectively calculating the dissipation coefficient and the instability coefficient of the forge piece at different pressing speeds, and calculating the average dissipation coefficient of the forge piece;
then, the pressing speed V with the average dissipation coefficient of 35-45% and no instability point is selectedtAs the optimum speed;
finally, V is storedtAnd will VtPerforming simulation calculation as the pressing speed of the next time step;
and circulating the steps until the forging die finishes the whole stroke, and outputting a forging die speed curve through a finite element program interface.
2. A forging die speed curve iterative optimization method based on a hot working diagram according to claim 1, wherein: the range of speeds allowed by the press is divided equally or logarithmically into 10 parts.
3. A forging die speed curve iterative optimization method based on a hot working diagram according to claim 1, wherein: the depression speed with the average dissipation factor closest to 40% was selected as the optimum depression speed.
4. A forging die speed curve iterative optimization method based on a hot working diagram according to claim 1, wherein: the forging die speed curve iteration optimization method can also be applied to an extrusion or heading process.
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