JP2011183417A - Method of evaluating stability of spring back - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of evaluating the stability of spring back of a press formed article. <P>SOLUTION: The stability of the spring back is evaluated by following steps: a forming analyzing step (S1) where the forming data of the press formed article are obtained; a step (S2) where at least one of the data of the physical property and the physical quantity in a part region of the press formed article is selected as a control factor and arithmetic processing is performed on the basis of the control factor; a step (S3) where the quantity of the spring back is calculated on the basis of the forming data and the forming data after the arithmetic processing; a step (S4) where S2 and S3 are repeatedly calculated to all selected control factors; a step (S5) where S1 to S4 are carried out in regard to forming conditions which are different from the above forming conditions and the SN ratio of the quantity of the spring back corresponding to the difference of the forming conditions is calculated about all calculated quantity of the spring back and a step (S6) where the stability of the spring back is determined on the basis of the calculated SN ratio. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for evaluating the stability of a springback generated in a press-formed product when a member for an automobile or the like is press-formed from a steel plate or a steel bar. Specifically, the present invention relates to a method for evaluating variation in the amount of springback using numerical analysis.

  Many automobile members such as doors, undercarriages, and body parts, home appliance members, building materials, and the like are manufactured by press-forming steel plates and steel bars. In recent years, in order to meet the demand for weight reduction of these members, press-formed products have been made thinner by using high-strength steel plates and steel bars as materials for press forming.

  However, with the increase in strength of steel plates and steel bars, springback is likely to occur due to the elastic recovery of the elastic deformation of steel plates and steel bars due to the residual stress present in the press-formed product after press forming. ing.

  On the other hand, for press-formed products, especially press-formed products used in automobiles, computer-aided CAE (Computer Aided Engineering) is actively used to reduce the cost and time required for design and development. .

  In addition, from the initial stage of design and development of press-molded products, concurrent engineering that takes into account quality variations during production has become common.

  Patent Document 1 discloses that a specific part to be analyzed is changed as a cause of the occurrence of springback in a press-molded product, and the amount of springback is minimized while numerically calculating physical property values and physical quantities of the specific part. Thus, there has been proposed a method for identifying a cause part of occurrence of springback and accurately deriving a physical property value / physical quantity of the cause part.

JP 2008-55476 A

  However, since the method described in Patent Document 1 aims to search for the shape of the press-molded product and the press-molding method that can minimize the amount of springback, the press-molded product was actually manufactured. It was not enough to examine the variation of the amount of springback at the initial stage of design and development of press-formed products.

  When actually manufacturing a press-molded product, the trim line shape and the method of press molding vary. Therefore, the control range is set for these variations. Of these variations, There are some factors that have a great influence on the springback of press-formed products.

  Factors that have a large effect on the springback of a press-formed product are investigated by performing test molding after the mold for molding the target press-formed product is completed, and the press is used to change the shape of the trim line. It has been common to improve the pass rate of a press-formed product at the time of manufacturing by modifying the shape of the mold or changing the method of press forming to reduce variations in the amount of springback.

  Therefore, in order to achieve the above-mentioned concurrent engineering, it was desired to study to reduce the variation in the amount of springback of the press-formed product at the time of manufacture, even in the initial stage of design and development of the press-formed product. The examination method was not established.

  The present invention provides a spring for a press-molded product that can reduce variations in the amount of spring-back of the press-molded product during manufacturing and study the stability of the spring back, even in the initial stage of the design and development of the press-molded product. An object of the present invention is to provide a back stability evaluation method.

  In view of the above situation, the present inventors calculated the quality of the springback amount calculated for each molding condition such as the trim line shape and the molding method when calculating the springback amount of the press-formed product by numerical analysis. The calculation of the S / N ratio of the springback amount used in the above was studied.

  As a result, the strain and stress generated in the press-molded product after press molding are numerically analyzed (molding analysis) for the entire press-molded product, and some of the press-molded products are expected to cause springback. With respect to the area of, the at least one of the physical property value and physical quantity data in the partial area is used as a control factor, the control factor is arithmetically processed, and the springback amount calculated based on the arithmetic processing result For all, it has been found that calculating and evaluating the S / N ratio of the springback amount with respect to the difference in molding conditions is a good method for evaluating the stability of the springback accurately and in a short period of time.

  The present invention has been completed with further improvements based on the above findings, and the gist thereof is as follows.

(1) A molding analysis step for numerically analyzing molding conditions for press molding to obtain molding data of a press molded product,
An arithmetic processing step of selecting at least one of physical property values and physical quantity data of a partial area of the press-molded product from the molding data of the press-molded product as a control factor, and performing arithmetic processing on the control factor When,
For the molding data and a partial area of the press-molded product, a springback amount calculating step for calculating a springback amount based on the molding data after the arithmetic processing;
Repeating the calculation processing step and the springback amount calculation step until the calculation processing step and the springback amount calculation step are executed for all the selected control factors;
For each of one or two or more molding conditions different from the molding conditions, the press molding analysis step, the calculation processing step, the springback amount calculation step, and the iterative calculation step are executed, and all of the calculated An SN ratio calculating step for calculating an SN ratio of the springback amount with respect to the difference in the molding conditions for the springback amount;
A springback stability determination step of determining the stability of the springback based on the calculated magnitude of the SN ratio;
A springback stability evaluation method, characterized by comprising:

(2) Level 1 that selects the same number of control factors as the number of columns of the orthogonal table of the experimental design method, and does not perform the arithmetic processing step on the control factors assigned to the columns of the orthogonal table; The method of evaluating springback stability according to (1) above, wherein the calculation processing step is executed according to a condition of each row of the orthogonal table to which a combination with level 2 for performing the calculation processing step is assigned. .

(3) The spring back stability evaluation method according to (2) above, wherein a mixed type orthogonal table of L12 is used as the orthogonal table.

(4) The springback stability evaluation method according to any one of (1) to (3), wherein the forming analysis step is numerically analyzed by an explicit method and the springback amount calculating step is numerically analyzed by an implicit method. .

  According to the present invention, not only when ordinary steel plates and steel bars are press-formed, but also when high-strength steel plates and steel bars such as high-tensile steel are press-formed, steel plates and steel bars are press-formed. The variation in the amount of springback that occurs at the time can be examined and evaluated in the design and development stage of the press-formed product, and the variation in the amount of springback in the press-formed product during manufacturing can be reduced.

  According to the present invention, in order to calculate the S / N ratio, the step of calculating the springback amount that must be repeatedly executed is numerically analyzed by the implicit method, and the molding analysis step of obtaining molding data that requires a long time for numerical analysis By analyzing numerically only by the explicit method, the stability of the spring back of the press-formed product can be evaluated in a shorter period of time, and the design and development man-hours of the press-formed product can be further reduced.

1 shows an example of a press-formed product targeted by the present invention. 1A is a perspective view, FIG. 1B is a plan view, and FIG. 1C is a front view. It is a flowchart explaining the springback stability evaluation method of this invention. FIG. 3A shows a trim line of a press-formed product, FIG. 3A is a perspective view showing a normal type trim line, and FIG. 3B is an enlarged type trim line. The residual stress removal site | part which is a control factor of Example 1 is shown. 4A is a front view, and FIG. 4B is a front view. The residual stress removal site | part which is a control factor of Example 2 is shown. FIG. 5A is a front view, and FIG. 5B is a front view.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an example of a press-formed product targeted by the present invention. 1A is a perspective view, FIG. 1B is a plan view, and FIG. 1C is a front view. In FIG. 1, the code | symbol 10 shows a press molded product.

  The press-formed product 10 includes a camber portion 12, a hat portion 13, a flange portion 14, a vertical wall portion 16, and a trim line 18. In the press-molded product 10, the camber portion 13 warps in the direction of the arrow ΔZ due to the spring back at the AA line in FIG. In FIG. 1B, reference numeral 20 denotes a press-formed product 10 before spring back, and reference numeral 21 denotes a press-formed product after spring back.

  FIG. 2 is a flowchart for explaining the springback stability evaluation method of the present invention. Hereinafter, the case where the springback stability evaluation method of the present invention is applied to the press-formed product 10 will be described for each step shown in FIG. In the above embodiment, the amount of spring back in FIG.

  The press-formed product 10 is formed by press-molding a blank material of a high-strength steel plate. However, the blank material is not limited to a high-strength steel plate, but of course a normal steel plate with respect to application of the springback stability evaluation method of the present invention. That is, a metal plate other than the steel material may be used.

(Step S1)
Step S1 uses the finite element method to determine the shape data (plate thickness, length, width, trim line, etc.) of the press-formed product 10 and the properties (strength, elongation, etc.) of the blank material (metal plate) to be used. , A shape such as a plate thickness) is set as a molding condition, and numerical analysis is performed to perform molding analysis to obtain molding data of the press-molded product 10.

  The molding data here means numerical data such as displacement, stress (residual stress), strain, and the like of the press-molded product 10 after press molding.

  In addition, if necessary, the molding conditions include die shape (die shape, punch width, curvature, diameter, etc., die-to-punch clearance), press pressure, blank material temperature during press and lubrication conditions. Etc. may be set.

  These molding conditions may be described in an input file of the finite element method software, or a step of inputting these molding conditions may be separately provided before step S1.

  The software of the finite element method can use a commercially available solver, and the finite element method model of the molding press product 10 may be defined by a shell element or a solid element according to the solver specification. It may be defined.

(Step S2)
Among the molding data obtained in step S1, at least one is selected as a control factor from the physical property values and physical quantities of a partial region of the press-molded product, and arithmetic processing is performed on the selected control factor.

  The physical property value here means the thickness, elastic modulus, plasticity coefficient, etc. of the blank material before molding the molded press product 10. The physical quantities referred to here are the displacement, stress (residual stress), strain numerical data (molding data) of the molding press product 10 after molding the blank material obtained in step S1, and these x, It shall mean each direction component of y and z or a shear direction component.

  In the above embodiment, the physical quantity is, for example, the stress of the press-molded product after press molding obtained in step S1, that is, the residual stress of the press-molded product 10.

  Then, the calculation processing in step S2 is to multiply the above-mentioned physical property values and physical quantities in the partial area of the press-formed product 10, for example, the flange portion 14, to make a constant value including zero, and to perform four arithmetic operations. That is, to calculate based on a function, to set an arbitrary value that is not constant.

  In the above embodiment, the arithmetic processing is, for example, processing for reducing the residual stress generated in the flange portion 14 of the press-formed product 10 to zero. Note that setting the residual stress of the flange portion 14 to zero corresponds to measures for providing a notch portion or a through hole in the flange portion 14 in an actual product.

(Step S3)
For the molding data obtained in step S1 and a partial area of the press-molded product 10, the springback amount is calculated using the finite element method based on the molding data after the arithmetic processing. Note that the springback amount is calculated according to a basic equation of finite elastic-plastic deformation or a discretization method, and the springback amount can be calculated in a short time.

(Step S4)
In step S2, at least one control factor is selected, but when two or more control factors are selected, it is necessary to execute steps S2 and S3 for all of the control factors.

  In the case of the press-formed product 10 of the above-described embodiment, there are two control factors, for example, the residual stress of the flange portion 14 and the residual stress of the vertical wall portion 18. Steps S2 and S3 are executed for these two control factors.

  Therefore, as shown in FIG. 2, when the first execution of steps S2 and S3 is completed, it is determined whether or not there is a control factor that does not execute steps S2 and S2.

  If there is a control factor that does not execute step S2 and step S3, the process returns to step S2, while if there is no control factor that does not execute step S2 and step S3 (step S2 for all control factors). If the execution of step S3 is completed), the process proceeds to step S5.

(Step S5)
The springback stability evaluation method of the present invention evaluates the stability of the springback based on the SN ratio of the springback amount with respect to the difference in molding conditions. It is necessary to select two or more different molding conditions, and for each of the two or more molding conditions, step S1, step S2, step S3, and step S4 are executed. The springback amount is calculated for each control factor, and the SN ratio of the springback amount with respect to the difference in molding conditions is calculated for all of these springback amounts.

  Therefore, when the execution of step S4 is completed and the process proceeds to step S5, as shown in FIG. 2, are step S1, step S2, step S3, and step S4 executed for all selected molding conditions? Judging.

  When Step S1, Step S2, Step S3, and Step S4 are not executed for all the selected molding conditions, the process returns to Step S1. On the other hand, Steps S1, S2, S3, When step S4 is executed, the SN ratio due to the difference in molding conditions is calculated based on all the springback amounts calculated so far.

  In the press-molded product 10 of the above-described embodiment, as a molding condition, for example, a case where two conditions of the trim line 18a and the enlarged trim line 18b are set as the shape of the trim line 18 will be described.

  FIG. 3 shows the trim line 18 of the press-formed product 10, FIG. 3 (a) is a perspective view showing a normal type trim line 18a, and FIG. 3 (b) is an enlarged type trim line 18b.

  The enlarged trim line 18b in FIG. 3B is a trim line that is enlarged by an enlarged portion 19 indicated by hatching in the longitudinal direction of the press-formed product 10 as compared with the normal trim line in FIG. It is.

  The shape of the trim line, in particular, the length in the longitudinal direction shown in FIG. 3 is likely to vary when the press-formed product 10 is manufactured. When this trim line is formed by enlarging only the enlarged portion 19 shown by oblique lines with respect to the shape of the press-molded product 10 according to the design drawing, that is, the shape of the normal die trim line 18a, that is, the enlarged die. When the press molded product 10 having the trim line 18b is formed, the difference in the shape of the trim line (the difference in the shape of the normal type trim line 18a and the enlarged type trim line 18b) is the amount of spring back of the press molded product 10. In order to investigate the influence on the variation in the shape, the molding conditions for the enlarged trim line 18b were set.

  Step S1, Step S2, Step S3, Step S4 and Step S5 are executed for each of the two conditions where the molding conditions are the normal type trim line 18a and the enlarged type trim line 18b, and the shape of the trim line is the normal type trim line. The SN ratio of the springback amount for the difference between 18a and the enlarged trim line 18b is calculated.

(Step S6)
Based on the S / N ratio calculated in step S5, the stability of the spring back of the press-formed product is determined. It can be determined that the larger the calculated S / N ratio, the smaller the variation in the amount of spring back of the press-formed product 10 during manufacturing, and the higher the stability of the spring back.

  Next, the selection of the control factor and the level for the selected control factor will be described. The control factors are assigned to the orthogonal table columns in the experimental design method, and the same number of control factors as the number of columns in the orthogonal table are selected.

  In the springback stability evaluation method of the present invention, the level for the control factor can be set in step S2.

  In the press-formed product 10 of the above embodiment, when the residual stress of the flange portion 14 is set as a control factor, the residual stress removal process is performed as level 1 and the residual stress removal process is performed as level 2, Step S2 is not executed, step S3 is executed based on the molding data of the stress (residual stress) calculated in step S1, and the springback is calculated. For the flange portion 14 which is a part of the area 10, a calculation process is performed in which the stress (residual stress) calculated in step S1 is zero, and a springback amount is calculated based on the molding data after the calculation process.

  In addition, when the level with respect to a control factor is made into 2 levels, it is preferable from a viewpoint of eliminating interaction that a orthogonal system uses a mixed system orthogonal table, such as L12.

  The level for the control factor is, for example, level 1 without residual stress removal processing, level 2 with residual stress removal processing, level 3 with residual stress removal processing, and in the case of level 2, at step S1 A calculation process for making the calculated stress (residual stress) zero is performed as a complete residual stress removal process. In the case of level 3, the stress (residual stress) calculated in step S1 is set to, for example, 1/3. It is also possible to perform a calculation process and to perform a partial residual stress removal process.

  In addition, when the level with respect to a control factor is made into 3 levels, it is preferable from a viewpoint which excludes an interaction, to use an orthogonal table for mixed system orthogonal tables, such as L18.

  In the actual press-formed product 10, complete residual stress removal is, for example, through hole provision, and partial residual stress removal is non-through hole provision.

  Next, the analysis time required for the step of performing numerical analysis in the springback stability evaluation method of the present invention will be described.

  The numerical analysis of the molding conditions of the press molding performed in step S1 is a numerical analysis of a phenomenon in which the press molding progresses with time and the blank material is deformed when the blank material is press-molded. It is preferable to use an explicit method in which the value of time t + Δt is obtained algebraically based on the value at time t and is repeated.

  On the other hand, since the calculation of the springback amount performed in step S3 is performed with the basic equation of finite elasto-plastic deformation and the content according to the discretization method, sufficient analysis accuracy can be obtained by the implicit method.

  The time required for the numerical analysis of the molding conditions of the press molding performed in step S1 is often a long time, but it may be performed once for one molding condition. Don't be. For example, in the above embodiment, each of the two conditions of the normal type trim line 18a and the enlarged type trim line 18b may be performed once.

  On the other hand, the calculation of the springback amount performed in step S3 requires one molding condition when the springback stability evaluation method of the present invention is performed based on the number of combinations of control factor levels, for example, an L12 orthogonal table. Run 12 times for. In the above embodiment, step S3 is executed 12 times for each of the two conditions of the normal trim line 18a and the enlarged trim line 18b. Therefore, in order to perform the springback stability evaluation method of the present invention, step S3 is performed. Must be executed 24 times.

  Therefore, it is preferable that step S3 with a large number of repetitions be an implicit method that can complete the execution time of one time in a short time. As described above, even if the calculation of the springback amount is an implicit method, the analysis accuracy of the springback amount does not decrease.

  Therefore, in the springback stability evaluation method according to the present invention, step S1 is an explicit method, and step S3 is an implicit method, so that only step S1 that requires a long analysis time is an explicit method. The stability of the springback can be evaluated in a shorter time while maintaining the above.

  Next, the present invention will be further described with reference to examples. Conditions in the examples are one example of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is examples of these one condition. It is not limited to. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

Example 1
The spring back stability evaluation method of the present invention was applied to the press-formed product 10 shown in FIG. 1, and the variation in the amount of spring back during press forming was evaluated by numerical analysis.

  The molding conditions were two conditions of the normal type trim line 18a and the enlarged type trim line 18b shown in FIGS. 3 (a) and 3 (b).

  The control factors are the stress (residual stress) removal of the flange portion 14 and the stress (residual stress) removal of the vertical wall portion 16 shown in FIG. Residual stress) was removed.

  Table 1 shows the control factors and levels of (Example 1). Table 2 shows an orthogonal table of (Example 1).

  Based on the orthogonal table of Table 2, the springback stability evaluation method of the present invention was applied to the press-formed product 10 according to the flowchart shown in FIG.

  Table 3 shows the amount of springback for each molding condition, that is, for each of the normal mold trim line 18a and the enlarged mold trim line 18b. Table 3 also shows the SN ratio to the difference in molding conditions, that is, the difference between the normal type trim line 18a and the enlarged type trim line 18b.

  As is clear from Table 3, when it is desired to minimize the amount of springback, the No. 1 is used for both the normal trim line 18a and the enlarged trim line 18a. It is best to remove the stress (residual stress) from only the vertical wall portion 16 without performing the stress (residual stress) removing process on the flange portion 14.

  On the other hand, when it is desired to reduce the variation in the amount of springback, No. 2 has the largest SN ratio with respect to the difference between the normal trim line 18a and the enlarged trim line 18a. It is best not to perform the stress (residual stress) removal process on the combination of 4, that is, any of the flange portion 14 and the vertical wall portion 16.

  That is, when the trim line 18 varies between the normal trim line 18a and the enlarged trim line 18b, no stress (residual stress) removal process is performed on either the flange portion 14 or the vertical wall portion 16. Sometimes, the variation in the amount of springback is no. 1-No. It becomes the smallest among the combinations of 4.

  In other words, in order to minimize the amount of springback, a measure is taken to prevent the residual stress from being present only in the vertical wall portion 16, for example, a shape in which notches are provided only in the vertical wall portion 16 is preferable. However, on the other hand, it means that the variation in the amount of springback increases. That is, at the time of manufacturing the press-molded product 10, it means that the dimensions of the press-molded product 10 often do not fall within the dimensional tolerance (a defective product often occurs).

  On the other hand, no stress (residual stress) removal process is performed on either the flange portion 14 or the vertical wall portion 16, that is, no notch or through hole is provided on either the flange portion 14 or the vertical wall portion 16. The shape reduces variations in the amount of springback. This means that the press-molded product 10 often falls within the dimensional tolerance when the press-molded product 10 is manufactured (the defective product is rarely generated).

  As described above, it was confirmed that the stability of the spring back of the press-formed product 10 can be evaluated by applying the present invention to the press-formed product 10.

(Example 2)
The spring back stability of the press-formed product 10 was evaluated in the same manner as in (Example 1) except that the mixed type orthogonal table of L12 was used.

  Table 4 shows control factors and levels of (Example 2). Table 5 shows an orthogonal table of (Example 2). In (Example 2), the residual stress removal site serving as a control factor is divided into five parts from the flange parts 14-1 to 14-5 for the flange part 14, and the vertical wall part 16-1 for the vertical wall part 16. It was divided into 6 to -16-6.

  Table 6 shows the results.

  As is apparent from Table 6, when it is desired to minimize the amount of springback, the No. 1 is used for both the normal trim line 18a and the enlarged trim line 18a. The combination of 2 is the best. On the other hand, when it is desired to reduce the variation in the amount of springback, No. 2 has the largest SN ratio with respect to the difference between the normal trim line 18a and the enlarged trim line 18a. Ten combinations are the best. Thus, it was confirmed that the stability of the spring back of the press-formed product 10 can be evaluated even when the L12 mixed orthogonal table is used.

  In addition, the place mentioned above is only what illustrated embodiment of this invention, and this invention can add a various change within the description range of a claim.

  As described above, according to the present invention, not only when a normal steel plate or steel bar is press-formed, but also when a high-strength steel plate or steel bar such as high-tensile steel is press-formed, The variation in the amount of springback that occurs when a steel bar is press-formed can be examined and evaluated at the design and development stage of the press-formed product, and the variation in the amount of springback in the press-formed product during manufacturing can be reduced. it can. The present invention has high utility value industrially.

  In addition, according to the present invention, in order to calculate the S / N ratio, a springback amount calculation step that must be repeatedly executed is numerically analyzed by an implicit method, and molding analysis that takes a long time for numerical analysis and obtains molding data By analyzing numerically only the steps using the explicit method and evaluating the stability of the spring back of the press-formed product in a shorter period of time, the design and development man-hours of the press-formed product can be further reduced. It has a great effect.

DESCRIPTION OF SYMBOLS 10 Press molded article 12 Camber part 14, 14-1, 14-2, 14-3, 14-4, 14-5 Flange part 16, 16-1, 16-2, 16-3, 16-4, 16- 5, 16-6 Vertical wall part 18 Trim line 18a Normal type trim line 18b Enlarged type trim line 19 Enlarged part 20 Press-formed product before spring back 21 Press-formed product after spring back

Claims (4)

Numerical analysis of press molding molding conditions, molding analysis step to obtain molding data of press molded products,
An arithmetic processing step of selecting at least one of physical property values and physical quantity data of a partial area of the press-molded product from the molding data of the press-molded product as a control factor, and performing arithmetic processing on the control factor When,
For the molding data and a partial area of the press-molded product, a springback amount calculating step for calculating a springback amount based on the molding data after the arithmetic processing;
Repeating the calculation processing step and the springback amount calculation step until the calculation processing step and the springback amount calculation step are executed for all the selected control factors;
For each of one or two or more molding conditions different from the molding conditions, the press molding analysis step, the calculation processing step, the springback amount calculation step, and the iterative calculation step are executed, and all of the calculated An SN ratio calculating step for calculating an SN ratio of the springback amount with respect to the difference in the molding conditions for the springback amount;
A springback stability determination step of determining the stability of the springback based on the calculated magnitude of the SN ratio;
A springback stability evaluation method characterized by comprising:   Select the same number of control factors as the number of columns in the orthogonal table of the experimental design method, and level 1 that does not perform the operation processing step for the control factors assigned to the columns of the orthogonal table; 2. The springback stability evaluation method according to claim 1, wherein the operation processing step is executed according to a condition of each row of the orthogonal table to which a combination with level 2 for performing the processing step is assigned.   The springback stability evaluation method according to claim 2, wherein a mixed orthogonal table of L12 is used as the orthogonal table.   4. The springback stability evaluation method according to claim 1, wherein the forming analysis step is numerically analyzed by an explicit method and the springback amount calculating step is numerically analyzed by an implicit method.

Images