CN109948215A - A kind of hot stamping process formulation method - Google Patents

Abstract

The invention provides a method for formulating a hot stamping process, which includes the following steps: Step 1, use three-dimensional modeling software to establish a geometric model of a part; Step 2, select material constitutive equations in finite element simulation software, and select several At an appropriate interval of n values, numerical simulation of the stamping process is carried out in turn, and the maximum value of the equivalent plastic strain is recorded; in the third step, the n value is the ordinate and the maximum equivalent strain is the abscissa, and the data points are drawn, and the data points are compared. Fitting is performed, and the obtained curve is regarded as the stamping criterion curve; Step 4, use the tensile test method to obtain the n-ε curve under various deformation conditions; Step 5, compare the n-ε curve with the stamping criterion curve Compare and obtain the best hot stamping process parameters for metal materials. The method of the invention is suitable for all metal materials, and has the advantages of short test period, low test cost and high penetration rate of test equipment.

Description

A kind of hot stamping process formulation method

technical field

The invention relates to the technical field of metallurgy, in particular to a method for formulating a hot stamping process.

Background technique

The hot stamping process refers to a stamping process that performs stamping deformation and then rapidly cools in a high temperature environment. It is mainly used to produce high-strength parts required for car sound. Compared with the original cold stamping, the hot stamping process has deformation The resistance is small, the plate is not easy to crack, the stamping precision is high, and the rebound amount after stamping deformation is small. Stamping temperature and deformation rate are the two most critical process parameters of hot stamping forming process. If the selection of process parameters is unreasonable, the sheet metal is prone to stamping cracking, so these two process parameters are of great significance for hot stamping deformation.

At present, there are two main methods for formulating the hot stamping process:

Method 1, the minimum temperature for complete austenitization of the steel sheet; for hot stamping of the steel sheet, the stamping deformation temperature is the minimum temperature for complete austenitization of the steel for stamping. The deformation temperature determined by this method is only the temperature at which the stamping deformation resistance is the smallest, not the temperature at which the steel plate has the maximum deformation capacity. The scope of application of this method is also very narrow, only applicable to steel materials.

Method 2, numerical simulation method; combine different stamping temperatures and stamping speeds to measure the stress-strain curves of stamping materials under various combination conditions, as well as the high-temperature forming limit curves at multiple temperatures. Then, under various deformation conditions, the finite element software is used to carry out numerical simulation of the stamping deformation process, and the calculation results of the simulated principal strain field are compared with the high temperature forming limit curve to determine the reasonable hot stamping process parameters. This method can exert the maximum deformation ability of the material. However, due to the large selection range of stamping temperature and stamping speed, there are many combination conditions and huge workload. If it is a complex-shaped part, the amount of calculation is quite huge, which will consume a lot of computing resources and a long computing time. In addition, due to the small number of equipment capable of measuring the high temperature forming limit curve, the test cost is high and the test cycle is long.

The above two methods have their limitations. The first method cannot exert the maximum deformation ability of the material itself, and is only suitable for steel materials. Method 2 has a huge workload and is time-consuming. Therefore, neither method can quickly and inexpensively determine the optimal thermoforming process for a material.

SUMMARY OF THE INVENTION

The technical task of the present invention is to provide a hot stamping process formulation method based on the work hardening index n value and finite element simulation in view of the above deficiencies of the prior art.

The technical scheme adopted by the present invention to solve the above-mentioned technical problems is: a method for formulating a hot stamping process, comprising the following steps:

The first step is to use 3D modeling software to establish the geometric model of the hot stamping finished part, and input the geometric model into the finite element simulation software;

The second step is to select the material constitutive equation in the form of equation (1) in the finite element simulation software;

σ=K· ^εn (1)

In the formula: the σ is the equivalent stress, the ε is the equivalent plastic strain, and the n is the work hardening index; the K value is an arbitrary number selected within a reasonable range; the K value is the final judgment of this method no effect on the result;

Select several n values within a reasonable numerical range, and then perform a stamping numerical simulation under each n value condition, and record the maximum value ε _p of the equivalent plastic strain ε in each simulation result;

In the third step, take the value of _n as the ordinate and the corresponding maximum value of plastic strain εp as the abscissa, draw these points in the two-dimensional plane coordinate system, and use equation (2) to calculate the numerical value of these points Fitting to get a curve as the criterion curve;

Step 4: Select the deformation temperature and deformation rate within a reasonable range, use a thermal simulation testing machine to conduct a thermal simulation tensile test, delete the elastic part and the necked part of each tensile stress-strain curve, and then carry out the remaining curves. Fitting filtering process, and finally for each curve, use equation (3) to calculate the n-ε curve of the material under various deformation conditions;

In step 5, compare the criterion curve obtained in step 3 with the n-ε curve obtained in step 4 in the same coordinate system. If the n-ε curve can pass through the criterion curve, it will appear in the criterion curve. On the right side, it means that the deformation conditions corresponding to the curve can ensure that stamping does not crack. If the n-ε curve cannot pass through the criterion curve, it means that stamping cracking will occur.

Further, the number of n values in the step 2 is 4-6.

Further, in the step 5, the higher the position of the n-ε curve in the coordinate system, the higher the stamping safety margin of the corresponding deformation condition.

In the hot stamping process formulation method of the present invention, only the Gleeble thermal simulation tester and less computing resources are used, and the optimum hot stamping process parameters and the optimum temperature of the metal material can be accurately determined without measuring the high temperature forming limit curve. and optimal deformation rate. Compared with the traditional method, the method of the present invention is suitable for all metal materials, and has the advantages of short test period, low test cost and high penetration rate of test equipment.

Description of drawings

1 is a schematic diagram of the theoretical basis of the present invention;

2 is a 3/4 geometric model diagram of a stamping part in an embodiment of the present invention;

FIG. 3 is a comparison diagram of the criterion curve in the embodiment of the present invention and the n-ε curve under different conditions.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

The theoretical basis of the method of the present invention is as follows:

The work hardening index n value can reflect the ability of the sheet to resist local thinning. The larger the n value, the stronger the ability of the sheet to resist local thinning during the stamping deformation process.

For example, if the criterion curve obtained by fitting is shown in Figure 1 after the third step of the present invention is completed, the physical meaning of any point A on the curve is: if the n value of the material is always 0.2, then in In the case of no local thinning, after the stamping is completed (point A), the plastic deformation of the material is 0.19 (abscissa of point A).

The n value of metal materials will gradually decrease with the increase of plastic strain, as shown in the material n-ε curve in Figure 1. This means that the n value of the material before point A is all greater than 0.2. The material with this mechanical property has a stronger resistance to local thinning than the BA curve, so after the stamping is completed, the maximum plastic deformation inside the material is generated. It must be less than 0.19.

At the same time, the n-ε curve can be extended to the right side of the criterion curve, and it can be determined that the material will not break before point A, and the plastic deformation amount that the material can withstand is greater than 0.19.

Therefore, as long as the n-ε curve of the material can extend to the right side of the criterion curve, it can be determined that the plastic deformation that the material can withstand is greater than the required plastic deformation, and the stamping process will not crack; on the contrary, if the material The n-ε curve does not extend to the right side of the criterion curve, and it can be determined that cracking will occur during the stamping process.

Example

The invention provides a method for formulating a hot stamping process, comprising the following steps:

The first step is to use 3D modeling software, such as UG and CATIA, to establish the geometric model of the stamping part (Figure 2), and input the geometric model into the finite element simulation software;

In the second step, the material constitutive equation in the form of equation (1) is selected in the finite element simulation software, and 4 n values with appropriate intervals are selected, and the numerical simulation of the stamping process is carried out in sequence. Four simulations were performed, and after the stamping was completed, the calculation results of the equivalent plastic strain field are shown in Table 1;

σ=K· ^εn (1)

Table 1 Calculation results of equivalent strain field

In the third step, take the n value as the ordinate and the maximum value of the equivalent plastic strain in the calculation result as the abscissa, draw 4 points in turn, and use equation (2) to fit these 4 points into a curve, as the judgment According to the curve, the criterion curve is shown in Figure 3.

Step 4: Select the deformation temperature and deformation rate within a reasonable range, use the thermal simulation testing machine Gleeble to conduct a thermal simulation tensile test, delete the elastic part and the necked part of each tensile stress-strain curve, and then analyze the remaining curves. Perform the fitting filtering process, and finally, for each curve, use equation (3) to calculate the n-ε curve of the material under various deformation conditions;

Step 5, superimpose the criterion curve obtained in step 3 and the n-ε curve obtained in step 4, and compare them in the same coordinate system, as shown in Figure 3:

The judgment results show that:

Under the process conditions (temperature 1000°C, deformation rate 8s ^-1 ), the corresponding curve cannot be stamped due to insufficient elongation;

Under the process conditions (temperature 1000°C, deformation rate 0.25s ^-1 ), (temperature 600°C, deformation rate 8s ^-1 ), (temperature 700°C, deformation rate 8s ^-1 ), although the elongation of the material is large, but Because the n value is too low, the above process conditions cannot complete the stamping;

Under the process conditions (temperature 800℃, deformation rate 8s ^-1 ), (temperature 900℃, deformation rate 8s ^-1 ), stamping can be successfully completed without cracking; process conditions (temperature 800℃, deformation rate 8s ^-1 ) The curve of n is above the curve of the process conditions (temperature 900°C, deformation rate 8s ^-1 ), and the value of n is larger, so its process conditions are better and it is the best process parameter.

In the method described in the present invention, the basic dimensions used in the calculation and test process need to be consistent.

The above descriptions are only the embodiments of the present invention, and are not intended to limit the scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the description and drawings of the present invention, or directly or indirectly applied to other related technologies Fields are similarly included in the scope of patent protection of the present invention.

Claims (3)

1. a kind of drop stamping technology establishment method, which comprises the steps of:

Step 1 establishes the geometrical model of drop stamping fabricated part using 3 d modeling software, and the geometrical model is input to In Finite Element Simulation Software；

Step 2 selects the material constitutive equation of equation (1) form in Finite Element Simulation Software；

σ=K εⁿ (1)

In formula: the σ is equivalent stress, and the ε is equivalent plastic strain, and the n is work hardening index；The K value be The arbitrary number chosen in reasonable range；K value is on the final judgement result of this method without influence；

Several n values are chosen in reasonable numberical range, then under the conditions of each n value, carry out a punching press Numerical-Mode It is quasi-, record the maximum value ε of the equivalent plastic strain ε in each analog result_p；

Step 3, using n value as ordinate, corresponding equivalent plastic strain maximum value ε_pAs abscissa, in two-dimensional surface These points are drawn in coordinate system, and these are put using equation (2) and carries out numerical fitting, obtain a curve, as criterion song Line；

Step 4 chooses deformation temperature and rate of deformation in reasonable range, carries out thermal simulation stretching using hot modeling test machine It tests, part after the elastic part and constriction of every tensile stress strain curve of deletion, then filtering is fitted to residual curve Processing is finally directed to every curve, calculates n- ε curve of material under the conditions of various modifications using equation (3)；

The n- ε curve that step 5, the criterion curve that step 3 is obtained and step 4 obtain, compares under the same coordinate system, If n- ε curve can pass through criterion curve, appears on the right side of criterion curve, then illustrate that the corresponding deformation condition of the curve can Guarantee that punching press is not cracked, if n- ε curve cannot pass through criterion curve, illustrates that stamping cracking phenomenon can occur.

2. a kind of drop stamping technology establishment method according to claim 1, which is characterized in that of n value in the step 2 Number is 4~6.

3. a kind of drop stamping technology establishment method according to claim 1, which is characterized in that in the step 5, n- ε is bent The position of line in a coordinate system is higher, and the secure ram nargin of corresponding deformation condition is higher.